Cross-linkers and their uses

ABSTRACT

Charged or pro-charged cross-linking moieties and conjugates of cell binding agents and drugs comprising the charged or pro-charged cross-linking moieties and method of making the same.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/911,571, filed Mar. 5, 2018; which is a continuation of Ser. No.15/293,579, filed Oct. 14, 2016, now abandoned; which is a continuationof U.S. patent application Ser. No. 14/713,419, filed May 15, 2015 andnow U.S. Pat. No. 9,498,541; which is a continuation of U.S. patentapplication Ser. No. 14/080,377, filed Nov. 14, 2013 and now U.S. Pat.No. 9,061,995; which is a continuation of U.S. patent application Ser.No. 13/542,126, filed Jul. 5, 2012 and now U.S. Pat. No. 8,613,930;which is a divisional of U.S. patent application Ser. No. 12/433,604,filed Apr. 30, 2009 and now U.S. Pat. No. 8,236,319; which claimspriority to U.S. Provisional Application No. 61/049,291, filed Apr. 30,2008, and to U.S. Provisional Application No. 61/147,966, filed Jan. 28,2009. The contents of all of the above-referenced applications areincorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to the synthesis of novel charged crosslinkers and cross linkers which can be processed by a target cell togive charged moieties. The present invention also relates to methods ofmaking cell-binding agent-drug conjugates comprising modification ofcell-binding agents with these cross-linkers, followed by reaction withdrugs, or modification of the drugs with these crosslinkers, followed byreaction with cell-binding agents. The improved method of makingconjugates provides the ability to link a higher number of drugmolecules per cell-binding agent resulting in greater potency andproviding greater aqueous solubility to the conjugates.

BACKGROUND OF THE INVENTION

The bifunctional modification reagent N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP) has been used to link two proteins together through adisulfide bond. The reagent is reacted with the first protein tointroduce an active disulfide-containing group in the modification step.A second protein, which contains a free thiol group, is then added toform a disulfide bond between the two proteins in the conjugation step.Many derivatives of SPDP and imide versions of SPDP have been described(U.S. Pat. No. 4,563,304; J. Carlsson et al. 173 Biochem. J. 723-737(1978); Goff D. A., Carroll, S. F. 1 BioConjugate Chem. 381-386 (1990);L. Delprino et al. 82 J. Pharm. Sci. 506-512 (1993); S. Arpicco et al.,8 BioConjugate Chem 327-337 (1997)).

Conjugates of cell-binding agents with highly cytotoxic drugs have beendescribed (U.S. Pat. Nos. 5,208,020, 5,416,064; 5,475,092, 5,585,499,6,436,931, 6,372,738 and 6,340,701; R. V. J. Chari et al., 52 CancerRes. 127-131 (1992)). In these conjugates, the cell-binding agents arefirst modified with a bifunctional agent such as SPDP, SPP or SMCC tointroduce an active disulfide or a maleimido moiety. Reaction with athiol-containing cytotoxic drug provides a conjugate in which thecell-binding agent, such as a monoclonal antibody, and drug are linkedvia disulfide bonds or thioether bonds.

Heterobifunctional cross-linkers comprising a nitropyridyldithio,dinitropyridyldithio, N.N-dialkylcarboxamidopyridyldithio ordi-(N.N-dialkylcarboxamido) pyridyldithio group and a reactivecarboxylic ester group such as a N-succinimidyl ester group or aN-sulfosuccinimidyl ester group have been described (U.S. Pat. No.6,913,748). The presence of a N-sulfosuccinimidyl group was claimed toprovide higher aqueous solubility to these cross-linkers. However, oncethe cell-binding agent has been reacted with these cross-linkers, theN-sulfosuccinimidyl group is displaced and the solubility advantage islost, both for the modified cell-binding agent and its drug conjugate.Since cytotoxic drugs used in cell-binding agent-drug conjugates areoften only sparingly soluble in aqueous solutions, it is often difficultto link a sufficient number of drug molecules to the cell-binding agentand still maintain aqueous solubility. In addition, reactions have to beconducted in dilute solutions, which are cumbersome to scale up becauseof the need to use large volumes of solution.

SUMMARY OF THE INVENTION

The present invention provides charged linkers, wherein the charges areretained both after modification of the cell-binding agent and in theresulting drug conjugate. More specifically, the present inventionrelates to the use of charged linkers to link drugs to a cell-bindingagent (e.g., an antibody). In one aspect of the invention, the chargedlinkers are used to modify cell-binding agents and link them to drugs.In another aspect of the invention, the charged linkers are used tomodify drugs and link them to cell-binding agents. In yet another aspectof the invention, the charged linkers are used to simultaneously linkdrugs and the cell-binding agents. In all instances, the preferred endresult is a drug-charged linker-cell-binding agent conjugate, which canbe represented by the formula, CB-(-L^(c)-D)_(q), wherein CB is acell-binding agent, L^(c) is a charged linker, D is a drug molecule, andq is an integer from 1 to 20. The presence of a charged group(s) in thelinker in the cell-binding agent-drug conjugate provides severaladvantages, such as i) greater water solubility of the final product,ii) ability to operate at a higher concentration in aqueous solutions,iii) ability to link a greater number of drug molecules per molecule ofcell-binding agent, resulting in higher potency, iv) potential for thecharged conjugate species to be retained inside the target cell,resulting in higher potency, and v) improved sensitivity of multidrugresistant cells, which would be unable to export the charged drugspecies from the cell. The invention also describes linkers, which canbe coupled to a drug and a cell binding agent to give a conjugate whichcan be metabolized in a cell to produce a drug metabolite containing oneor more charged moieties. These linkers will be referred to aspro-charged linkers. Moieties of the linker which will become chargedafter cell processing will be referred to as pro-charged moieties.

In one aspect of the present invention, the charged or pro-charged crosslinker is represented by formula (I) wherein Y′ can react with acell-binding agent and Q can react with a cytotoxic drug:

wherein:

Y′ represents a functional group that enables reaction with acell-binding agent;

Q represents a functional group that enables linkage of a cytotoxic drugvia a disulfide, thioether, thioester, peptide, hydrazone, ether, ester,carbamate or amide bond;

R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, and R₁₀ are the same or differentand are H, linear alkyl having from 1-6 carbon atoms, branched or cyclicalkyl having from 3 to 6 carbon atoms, linear, branched or cyclicalkenyl or alkynyl having from 2 to 6 carbon atoms, anions, such as butnot limited to, SO₃ ⁻, X—SO₃ ⁻, OPO₃ ²⁻, X—OPO₃ ²⁻, PO₃ ²⁻, X—PO₃ ²⁻,CO₂ ⁻, and cations, such as but not limited to, a nitrogen containingheterocycle, N⁺R₁₁R₁₂R₁₃ or X—N⁺R₁₁R₁₂R₁₃, or a phenyl, wherein:

R₁₁, R₁₂ and R₁₃ are the same or different and are H, linear alkylhaving from 1 to 6 carbon atoms, or branched or cyclic alkyl having from3 to 6 carbon atoms and X represents phenyl or a linear alkyl havingfrom 1 to 6 carbon atoms, or a branched or cyclic alkyl having from 3 to6 carbon atoms;

l, m and n are 0 or an integer from 1 to 4; and

A is a phenyl or a substituted phenyl, wherein the substituent is alinear alkyl having from 1 to 6 carbon atoms, or a branched or cyclicalkyl having from 3 to 6 carbon atoms, or a charged substituent selectedfrom anions, such as but not limited to, SO₃ ⁻, X—SO₃ ⁻, OPO₃ ²⁻, X—OPO₃²⁻, PO₃ ²⁻, X—PO₃ ²⁻, CO₂ ⁻, and cations, such as but not limited to, anitrogen containing heterocycle, N⁺R₁₁R₁₂R₁₃ or X—N⁺R₁₁R₁₂R₁₃, wherein Xhas the same definition as above, and wherein g is 0 or 1;

Z is an optional polyethyleneoxy unit of formula (OCH₂CH₂)_(p), whereinp is 0 or an integer from 2 to about 1000, or F1-E1-P-E2-F2 unit inwhich E1 and E2 are the same or different and are C═O, O, or NR₁₄,wherein R₁₄ is H, a linear alkyl having from 1-6 carbon atoms, abranched or cyclic alkyl having from 3 to 6 carbon atoms, a linear,branched or cyclic alkenyl or alkynyl having from 2 to 6 carbon atoms; Pis a peptide unit between 2 and 20 amino acids in length, wherein E1 orE2 can be linked to the peptide through the terminal nitrogen, terminalcarbon or through a side chain of one of the amino acids of the peptide;and F1 and F2 are the same or different and are an optionalpolyethyleneoxy unit of formula (OCH₂CH₂)_(p), wherein p is 0 or aninteger from 2 to about 1000, provided that when Z is not F1-E1-P-E2-F2,at least one of R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, and R₁₀ is a chargedsubstituent or when g is 1, at least one of A, R₁, R₂, R₃, R₄, R₅, R₆,R₇, R₈, R₉, and R₁₀ is a charged substituent.

In another aspect, the present invention provides a cell-bindingagent-drug conjugate of formula (II), in which the cell-binding agent,CB, and the drug, D, have reacted at the two ends of the charged orpro-charged cross linker:

wherein:

CB represents a cell-binding agent;

D represents the drug linked to the cell-binding agent by a disulfide,thioether, thioester, peptide, hydrazone, ether, ester, carbamate, oramide bond;

R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, and R₁₀ are the same or differentand are H, linear alkyl having from 1-6 carbon atoms, branched or cyclicalkyl having from 3 to 6 carbon atoms, linear, branched or cyclicalkenyl or alkynyl having from 2 to 6 carbon atoms, anions, such as butnot limited to, SO₃ ⁻. X—SO₃ ⁻. OPO₃ ²⁻, X—OPO₃ ²⁻, PO₃ ²⁻, X—PO₃ ²⁻,CO₂ ⁻, cations, such as but limited to, a nitrogen containingheterocycle, N⁺R₁₁R₁₂R₁₃ or X—N⁺R₁₁R₁₂R₁₃, or a phenyl, wherein:

R₁₁, R₁₂ and R₁₃ are the same or different and are H, linear alkylhaving from 1 to 6 carbon atoms, branched or cyclic alkyl having from 3to 6 carbon atoms and X represents phenyl or a linear alkyl having from1 to 6 carbon atoms, or a branched or cyclic alkyl having from 3 to 6carbon atoms;

l, m and n are 0 or an integer from 1 to 4; and

A is a phenyl or substituted phenyl, wherein the substituent is a linearalkyl having from 1 to 6 carbon atoms, or a branched or cyclic alkylhaving from 3 to 6 carbon atoms, or a charged substituent selected fromanions, such as but not limited to, SO₃ ⁻. X—SO₃ ⁻. OPO₃ ²⁻, X—OPO₃ ²⁻,PO₃ ²⁻, X—PO₃ ²⁻, CO₂—, cations, such as but not limited to, a nitrogencontaining heterocycle, N⁺R₁₁R₁₂R₁₃ or X—N⁺R₁₁R₁₂R₁₃, wherein X has thesame definition as above, and wherein g is 0 or 1;

Z is an optional polyethyleneoxy unit of formula (OCH₂CH₂)_(p), whereinp is 0 or an integer from 2 to about 1000, or F1-E1-P-E2-F2 unit inwhich E1 and E2 are the same or different and are C═O, O, or NR14,wherein R₁₄ is H, a linear alkyl having from 1-6 carbon atoms, abranched or cyclic alkyl having from 3 to 6 carbon atoms, a linear,branched or cyclic alkenyl or alkynyl having from 2 to 6 carbon atoms; Pis a peptide unit between 2 and 20 amino acids in length, wherein E1 orE2 can be linked to the peptide through the terminal nitrogen, terminalcarbon or through a side chain of one of the amino acids of the peptide;and F1 and F2 are the same or different and are an optionalpolyethyleneoxy unit of formula (OCH₂CH₂)_(p), wherein p is 0 or aninteger from 2 to about 1000, provided that when Z is not F1-E1-P-E2-F2,at least one of R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, and R₁₀ is a chargedsubstituent or when g is 1, at least one of A, R₁, R₂, R₃, R₄, R₅, R₆,R₇, R₈, R₉, and R₁₀ is a charged substituent;

Y represents a carbonyl, thioether, amide, disulfide, or hydrazonegroup; and q represents an integer from 1 to 20.

In a further aspect, the present invention provides a modifiedcell-binding agent of formula (III), in which the cell-binding agent,CB, has reacted with the cross linker, which still has Q, a groupcapable of reacting with a cytotoxic drug:

wherein the substituents are as defined above.

In an even further aspect, the present invention provides a modifieddrug of formula (IV), in which the drug, D, has reacted with the crosslinker, which still has Y′, a group capable of reacting with thecell-binding agent:

wherein the substituents are as defined above.

The present invention further relates to a method of making acell-binding agent drug conjugate of formula (II), wherein the drug islinked to a cell-binding agent via a charged or pro-charged linker.

The present invention also relates to a method of making a modifiedcell-binding agent of formula (III), wherein the cell-binding agent isreacted with the charged or pro-charged linker.

The present invention also relates to a method of making a modified drugof formula (IV), wherein the drug is reacted with the charged orpro-charged linker.

The present invention includes a composition (e.g., a pharmaceuticalcomposition) comprising conjugates or derivatives thereof (and/orsolvates, hydrates and/or salts thereof) and a carrier (apharmaceutically acceptable carrier). The present invention alsoincludes a composition (e.g., a pharmaceutical composition) comprisingconjugates or derivatives thereof, (and/or solvates, hydrates and/orsalts thereof) and a carrier (a pharmaceutically acceptable carrier),further comprising a second therapeutic agent. The present compositionsare useful for inhibiting abnormal cell growth or treating aproliferative disorder in a mammal (e.g., human).

The present invention includes a method of inhibiting abnormal cellgrowth or treating a proliferative disorder in a mammal (e.g., human)comprising administering to said mammal a therapeutically effectiveamount of the conjugates or derivatives thereof, (and/or solvates andsalts thereof) or a composition thereof, alone or in combination with asecond therapeutic agent.

The compounds of this invention, derivatives thereof, or conjugatesthereof, and compositions comprising them, are useful for treating orlessening the severity of disorders, such as, characterized by abnormalgrowth of cells (e.g., cancer). Other applications for compounds orconjugates of this invention include, but are not limited to, treatingosteoporosis, depression, anxiety, stress, phobias, panic, dysphoria,psychiatric disorders, and pain or as antiepileptics, antibacterials,diuretics and hypotensives, hypolipidemics, and anti-depressants.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the synthesis of sulfonic acid-containing cross-linkingreagents that contain a nitropyridyldisulfide group and a reactivecarboxylic acid ester. Hydroxyalkanoate esters are first converted intodibromoalkanoate esters as shown, followed by conversion of the α-bromosubstituent into a sulfonic acid.

FIG. 2 shows the synthesis of sulfonic acid-containing cross-linkingreagents that contain a pyridyldisulfide group and a reactive carboxylicacid ester.

FIGS. 3, 4 and 5 show various routes for the synthesis of chargedcross-linking agents bearing a reactive carboxylic acid ester andmaleimido substituent, enabling linkage via thioether bonds.

FIGS. 6 and 7 show the synthesis of phosphate-containing cross-linkingreagents that contain a pyridyldisulfide group and a reactive carboxylicacid ester.

FIG. 8 shows the synthesis of phosphate-containing cross-linkingreagents that contain a nitropyridyldisulfide group and a reactivecarboxylic acid ester

FIGS. 9 and 10 show different routes for the synthesis ofphosphate-containing charged cross-linking agents bearing a reactivecarboxylic acid ester and a maleimido substituent, enabling linkage viathioether bonds.

FIG. 11 shows the synthesis of sulfonic acid-containing cross-linkingreagents, where the sulfonate substituent is attached to a branchedalkyl group. These reagents also bear a pyridyldisulfide group and areactive carboxylic acid ester.

FIG. 12 shows the synthesis of sulfonic acid-containing cross-linkingreagents, where the sulfonate substituent is attached to a branchedalkyl group. These reagents also bear a reactive carboxylic acid esterand a maleimido group that allows for linkage via thioether bonds.

FIG. 13 shows the synthesis of quartenary amine-containing cross-linkingreagents that contain a pyridyldisulfide group and a reactive carboxylicacid ester.

FIG. 14 shows the synthesis of quartenary amine cross-linking agentsbearing a reactive carboxylic acid ester and maleimido substituent,enabling linkage via thioether bonds.

FIG. 15 shows the synthesis of sulfonic acid-containing cross-linkingreagents that contain a pyridyldisulfide group and a reactive carboxylicacid ester. In these compounds, the sulfonate substituent is on thecarbon atom on the position β to the carboxyl ester.

FIG. 16 shows the synthesis of phosphate-containing cross-linkingreagents that contain a pyridyldisulfide group and a reactive carboxylicacid ester. In these compounds, the phosphate substituent is on theβ-position relative to the carboxyl ester.

FIGS. 17, 18 and 19 show the synthesis of various sulfonicacid-containing cross-linking reagents that contain a polyethyleneglycol(PEG) chain, along with a nitropyridyldisulfide group and a reactivecarboxylic acid ester.

FIGS. 20 and 21 show the synthesis of various sulfonic acid-containingcross-linking reagents that contain a polyethyleneglycol (PEG) chain,along with a maleimido group and a reactive carboxylic acid ester.

FIG. 22 shows the synthesis of phosphate-containing cross-linkingreagents, where the phosphate substituent is attached to an aromaticgroup. These reagents also bear a reactive carboxylic acid ester and anitropyridyldithio group that allows for linkage via disulfide bonds.

FIG. 23 shows the synthesis of phosphate-containing cross-linkingreagents, where the phosphate substituent is attached to a branchedalkyl group. These reagents also bear a reactive carboxylic acid esterand a nitropyridyldithio group that allows for linkage via disulfidebonds.

FIGS. 24-31 show the synthesis of sulfonate-containing cross-linkingreagents that also incorporate a hydrazide moiety allowing for linkagevia acid-labile bonds.

FIGS. 32-36 show the synthesis of phosphate-containing cross-linkingreagents that also incorporate a hydrazide moiety allowing for linkagevia acid-labile bonds.

FIGS. 37-38 show the synthesis of quartenary amine-containingcross-linking reagents that also incorporate a hydrazide moiety allowingfor linkage via acid-labile bonds.

FIGS. 39-42 show the synthesis of charged cross-linking reagents thatalso incorporate a polyethyleneglycol (PEG) moiety.

FIGS. 43-44 show the synthesis of phosphate-containing cross-linkingreagents, where the phosphate substituent is attached to an aromaticresidue or to an alkyl group. These reagents also bear a reactivecarboxylic acid ester and a nitropyridyldithio group that allows forlinkage via disulfide bonds.

FIGS. 45-49 show the synthesis of charged cross-linking agents bearingreactive carboxylic acid ester and a haloacetyl substituent, enablinglinkage via thioether bonds.

FIG. 50 shows the synthesis of a procharged linker that would generate anegatively charged carboxylate metabolite.

FIG. 51 shows a conjugate of linker 158 to a drug and a monoclonalantibody and how the conjugate would be processed in the lysosome of atarget cell to give a metabolite containing the drug bearing anegatively charged carboxylate.

FIG. 52 shows the synthesis of a procharged linker that would generate apositively charged amine-containing metabolite.

FIG. 53 shows a conjugate of a procharged linker to a drug and amonoclonal antibody and how the conjugate would be processed in thelysosome of a target cell to give a metabolite of the drug bearing apositively charged amine.

FIG. 54 shows the synthesis of a procharged linker that would generate acharged carboxylate metabolite.

FIG. 55 shows a conjugate of linker 172 to a drug and a moloclonalantibody and how the conjugate would be processed in the lysosome of atarget cell to give a metabolite containing the drug bearing acarboxylic acid and a lysine residue.

FIG. 56 shows the use of charged linker in modifying a cell-bindingagent and producing a cell-binding agent-drug conjugate bearing acharged linker.

FIGS. 57A, 57B and 57C show the in vitro potency of cell-bindingagent-drug conjugates in which a charged crosslinker is incorporated.

FIG. 58 shows the in vitro potency and target selectivity ofcell-binding agent-drug conjugates bearing a charged crosslinker.

FIG. 59 shows the mass spectrum of cell-binding agent-drug conjugatesbearing a charged crosslinker.

FIG. 60 shows the cytotoxicity of Anti-CanAg (huC242)-sulfonatelinker-maytansinoid conjugates with increasing maytansinoids load (E:A)toward COLO205 cells.

FIG. 61 shows the cytotoxicity of Anti-CanAg (huC242)-sulfonatelinker-maytansinoid conjugates with increasing maytansinoids load (E:A)toward multi-drug resistant COLO205-MDR cells.

FIG. 62 compares cytotoxicity of Anti-CanAg (huC242)-maytansinoidconjugates with or without sulfonate group in the linker towardmulti-drug resistant COLO205-MDR cells.

FIG. 63 compares the cytotoxicity of Anti-EpCAM (B38.1)-maytansinoidconjugates with or without sulfonate group in linker toward multi-drugresistant COLO205-MDR cells.

FIG. 64 compares the cytotoxicity of Anti-EpCAM (B38.1)-maytansinoidconjugates with or without sulfonate group in linker toward multi-drugresistant HCT15 cells.

FIG. 65 compares the cytotoxicity of Anti-EpCAM (B38.1)-maytansinoidconjugates with or without sulfonate group in linker toward multi-drugresistant COLO205-MDR cells.

FIG. 66 shows the in vivo anti-tumor activity of anti-EpCAMantibody-maytansinoid conjugates on COLO205 mdr xenografts (individualtumors).

FIG. 67 shows the in vivo anti-tumor activity of anti-EpCAMantibody-maytansinoid conjugates on COLO205 xenografts (individualtumors).

FIGS. 68-70 show the methods of synthesis of sulfonic acid-containingcross-linking reagents. These reagents bear a reactive carboxylic acidester and a maleimido group that allows for linkage via thioether bonds.

FIG. 71 shows the methods of synthesis of quartenary amine-containingcross-linking reagents. These reagents also bear a reactive carboxylicacid ester and a pyridyldithio group that allows for linkage viadisulfide bonds.

FIGS. 72A and 72B show Plasma pharmacokinetics of huC242Antibody-Sulfo-Mal-[³H-labeled]-DM4 conjugates with 3.5 DM4/Ab or 6.4DM4/Ab dosed at 12.9 mg/kg and 7.9 mg/kg (i.v.) respectively in CD-1mice.

FIG. 72A. shows Ab concentrations (measured by ELISA or by 3H counts)versus time after administration. FIG. 72B. shows Maytansinoid(DM4)/Antibody (Ab) ratio versus time after administration.

In FIGS. 1-71, where applicable, n reperesents 0 or an integer from 1 to10, and m represents 0 or an integer from 1 to 2000.

DETAILED DESCRIPTION OF THE INVENTION

The novel conjugates disclosed herein use charged or pro-chargedcross-linkers. Examples of some suitable cross-linkers and theirsynthesis are shown in FIGS. 1 to 10. Preferably, the charged orpro-charged cross-linkers are those containing sulfonate, phosphate,carboxyl or quaternary amine substituents that significantly increasethe solubility of the modified cell-binding agent and the cell-bindingagent-drug conjugates, especially for monoclonal antibody-drugconjugates with 2 to 20 drugs/antibody linked. Conjugates prepared fromlinkers containing a pro-charged moiety would produce one or morecharged moieties after the conjugate is metabolized in a cell.

Cross-Linkers

The synthetic routes to produce charged crosslinkers of the presentinvention are shown in FIGS. 1-49. Synthetic routes to produce linkerswith pro-charged moieties are shown in FIGS. 50, 52, and 54. FIGS. 51,53 and 55 show a conjugate of each of the respective pro-charged linkerswith a drug and a monoclonal antibody and how these conjugates would bemetabolized in a target cell to give charged metabolites. Thecrosslinkers possess three elements: a) a substituent that is eithercharged or will become charged when conjugates employing these linkersare metabolized in cells. The charge will be either anionic, such as butnot limited to, carboxylate, sulfonate or phosphate, or cationic, suchas but not limited to, a tertiary, quaternary, or primary amine or anitrogen-containing heterocycle, b) a group, such as aN-hydroxysuccimimide ester, maleimido group, haloacetyl group, andhydrazide, capable of reaction with a cell-binding agent, and c) agroup, such as but not limited to, a disulfide, maleimide, haloacetyl,and hydrazide, capable of reaction with a drug. The charged orpro-charged substituent can be introduced by methods described herein.For example, a sulfonate charge can be introduced by first treating acommercially available haloester compound with thioacetate to produce athioacetyl compound, followed by oxidation of the thioacetyl group,using hydrogen peroxide, to a sulfonate group. Phosphate containingcrosslinkers can be synthesized by methods described herein. First thedesired reactive group, such as but not limited to, thiol, maleimide,haloacetyl and hydrazide, is introduced by the reactions shown in FIGS.6-10, followed by hydrolysis of the phosphate ester to give the chargedcrosslinker bearing a phosphate. A positively charged quaternary aminesubstituent can be introduced in the crosslinker by reaction of an aminewith an α,β-unsaturated ketone (see, for example, FIGS. 13 and 37).Alternatively a charged amine substituent can be introduced bydisplacement of a halogen with the amine or nitrogen containingheterocycle of choice.

Preferably, the cross-linkers are compounds of the formula (I) below:

wherein Y′ represents a functional group that enables reaction with acell-binding agent;

Q represents a functional group that enables linkage of a drug via adisulfide, thioether, thioester, peptide, hydrazone, ester, ether,carbamate or amide bond;

R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, and R₁₀ are the same or differentand are H, linear alkyl having from 1-6 carbon atoms, branched or cyclicalkyl having from 3 to 6 carbon atoms, linear, branched or cyclicalkenyl or alkynyl having from 2 to 6 carbon atoms, anions, such as butnot limited to, SO₃ ⁻, X—SO₃ ⁻, OPO₃ ²⁻, X—OPO₃ ²⁻, PO₃ ²⁻, X—PO₃ ²⁻,CO₂—, cations, such as but not limited to, a nitrogen containingheterocycle, N⁺R₁₁R₁₂R₁₃ or X—N⁺R₁₁R₁₂R₁₃ or a phenyl, wherein:

R₁₁, R₁₂ and R₁₃ are the same or different and are H, linear alkylhaving from 1 to 6 carbon atoms, or branched or cyclic alkyl having from3 to 6 carbon atoms and X represents phenyl or a linear alkyl havingfrom 1 to 6 carbon atoms, or a branched or cyclic alkyl having from 3 to6 carbon atoms;

l, m and n are 0 or an integer from 1 to 4;

A is a phenyl or substituted phenyl, wherein the substituent is a linearalkyl having from 1 to 6 carbon atoms, or a branched or cyclic alkylhaving from 3 to 6 carbon atoms, or a charged substituent selected fromanions, such as but not limited to, SO₃ ⁻. X—SO₃ ⁻. OPO₃ ²⁻, X—OPO₃ ²⁻,PO₃ ²⁻, PO₃ ²⁻, CO₂—, and cations, such as but not limited to, anitrogen containing heterocycle, N⁺R₁₁R₁₂R₁₃ or X—N⁺R₁₁R₁₂R₁₃, wherein Xhas the same definition as above, and wherein g is 0 or 1;

Z is an optional polyethyleneoxy unit of formula (OCH₂CH₂)_(p), whereinp is 0 or an integer from 2 to about 1000, or F1-E1-P-E2-F2 unit inwhich E1 and E2 are the same or different and are C═O, O, or NR14,wherein R₁₄ is H, a linear alkyl having from 1-6 carbon atoms, abranched or cyclic alkyl having from 3 to 6 carbon atoms, a linear,branched or cyclic alkenyl or alkynyl having from 2 to 6 carbon atoms; Pis a peptide unit between 2 and 20 amino acids in length, wherein E1 orE2 can be linked to the peptide through the terminal nitrogen, terminalcarbon or through a side chain of one of the amino acids of the peptide;and F1 and F2 are the same or different and are an optionalpolyethyleneoxy unit of formula (OCH₂CH₂)_(p), wherein p is 0 or aninteger from 2 to about 1000, provided that when Z is not F1-E1-P-E2-F2,at least one of R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, and R₁₀ is a chargedsubstituent or when g is 1, at least one of A, R₁, R₂, R₃, R₄, R₅, R₆,R₇, R₈, R₉, and R₁₀ is a charged substituent.

Examples of the functional group, Y′, that enables reaction with acell-binding agent include amine reacting agents such as but not limitedto N-hydroxysuccinmide esters, p-nitrophenyl esters, dinitrophenylesters, pentafluorophenyl esters; thiol reactive agents such as but notlimited to pyridyldisulfides, nitropyridyldisulfides, maleimides,haloacetates and carboxylic acid chlorides.

Examples of the functional group, Q, which enables linkage of acytotoxic drug, include groups that enable linkage via a disulfide,thioether, thioester, peptide, hydrazone, ester, carbamate, or amidebond. Such functional groups include, but are not limited to, thiol,disulfide, amino, carboxy, aldehydes, maleimido, haloacetyl, hydrazines,and hydroxy.

Examples of linear alkyls include methyl, ethyl, propyl, butyl, pentyland hexyl. Examples of branched or cyclic alkyls having 3 to 6 carbonatoms include isopropyl, sec-butyl, isobutyl, tert-butyl, pentyl, hexyl,cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl.

Examples of linear alkenyls having 2 to 6 carbon atoms include ethenyl,propenyl, butenyl, pentenyl, hexenyl. Examples of branched or cyclicalkenyls having 2 to 6 carbon atoms include isobutenyl, isopentenyl,2-methyl-1-pentenyl, 2-methyl-2-pentenyl.

Examples of linear alkynyls having 2 to 6 carbon atoms include ethynyl,propynyl, butynyl, pentynyl, hexynyl. Examples of branched or cyclicalkynyls having up to 6 carbon atoms include 3-methyl-1-butynyl,3-methyl-1-penynyl, 4-methyl-2-hexynyl.

In preferred embodiments, one of R₁, R₂, R₃, R₄, R₉, R₁₀ is a chargedsubstituent selected from sulfonate, phosphate or trialkylammonium, andthe rest are H, l, g and m are each 0, n=1, Q and Y′ are eachindependently, a disulfide substituent, a maleimido, a haloacetyl group,or a N-hydroxy succinimide ester. In another more preferred embodiment,one of R₁, R₂, R₃, R₄, R₉, R₁₀ is a sulfonate, and the rest are H, l, gand m are each 0, n=1, Q is a disulfide, maleimido or haloacetyl moiety,and Y′ is a maleimido moiety or a N-hydroxy succinimide ester. In afurther more preferred embodiment, one of R₁, R₂, R₃, R₄, R₉, R₁₀ is asulfonate, and the rest are H, 1, g and m are each 0, n=1, Q is apyridyldithio or nitropyridyldithio group, maleimido or haloacetylmoiety, and Y′ is a N-hydroxy succinimide ester.

The synthesis of 2-dithionitropyridyl and 2-dithio-dinitropyridylcontaining cross-linkers of formulae (I) is shown, for example, in FIGS.1, 2 and the synthesis of the corresponding 4-dithionitropyridyl and4-dithio-dinitropyridyl containing cross-linkers of the formula (I) isshown, for example, in FIG. 6. The synthesis of maleimido-containingcharged cross linkers of the formula (I) with a sulfonate group isshown, for example, in FIGS. 3, 4 and 5. The synthesis ofmaleimido-containing charged cross linkers of the formula (I) with aphosphate group is shown, for example, in FIGS. 9 and 10. The synthesisof quaternary amine-containing charged crosslinkers of formula (I) isshown, for example, in FIGS. 13 and 14. The synthesis of polyethyleneglycol-containing charged cross linkers of formula (I) are shown, forexample, in FIGS. 17-21. The synthesis of charged cross linkers offormula (I) bearing a hydrazide moiety enabling linkage via acid-labilebonds is shown, for example, in FIGS. 24-36.

Cell-Binding Agent Drug-Conjugates

Using the charged or pro-charged crosslinkers a high number (>6) of drugmolecules can be introduced. In non limiting examples, FIG. 57exemplifies that cell-binding agent-drug conjugates prepared using acharged crosslinker of the present invention display high potency. Inaddition, the potency is target selective (see, for example, FIG. 58),since, even after linkage of a high number of drug molecules, theconjugate is highly potent towards target cells, but much less potenttowards non-target cells. As exemplified in FIG. 59, mass spectralanalysis demonstrates that the drugs are linked covalently to thecell-binding agent via the charged crosslinker.

The conjugates of the present invention can be represented by thefollowing formula, CB-(-L^(c)-D)_(q), wherein CB is a cell-bindingagent, L^(c) is a charged or pro-charged linker, D is a drug molecule,and q is an integer from 1 to 20.

Preferably, the conjugates have the following formula (II):

wherein CB represents a cell-binding agent,

D represents a drug linked to the cell-binding agent by a disulfide,thioether, thioester, peptide, hydrazone, ester, carbamate or amidebond;

R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, and R₁₀ are the same or differentand are H, linear alkyl having from 1-6 carbon atoms, branched or cyclicalkyl having from 3 to 6 carbon atoms, linear, branched or cyclicalkenyl or alkynyl having from 2 to 6 carbon atoms, anions, such as butnot limited to, SO₃ ⁻. X—SO₃ ⁻. OPO₃ ²⁻, X—OPO₃ ²⁻, PO₃ ²⁻, X—PO₃ ²⁻,CO₂ ⁻, cations, such as but not limited to, a nitrogen containingheterocycle, N⁺R₁₁R₁₂R₁₃ or X—N⁺R₁₁R₁₂R₁₃, or a phenyl, wherein:

R₁₁, R₁₂ and R₁₃ are same or different and are H, linear alkyl havingfrom 1 to 6 carbon atoms, branched or cyclic alkyl having from 3 to 6carbon atoms and X represents phenyl or a linear alkyl having from 1 to6 carbon atoms, or a branched or cyclic alkyl having from 3 to 6 carbonatoms;

l, m and n are 0 or an integer from 1 to 4;

A is a phenyl or substituted phenyl, wherein the substituent is a linearalkyl having from 1 to 6 carbon atoms, or a branched or cyclic alkylhaving from 3 to 6 carbon atoms, or a charged substituent selected fromanions, such as but not limited to, SO₃ ⁻. X—SO₃ ⁻. OPO₃ ²⁻, X—OPO₃ ²⁻,PO₃ ²⁻, PO₃ ²⁻, CO₂ ⁻, cations, such as but not limited to, a nitrogencontaining heterocycle, N⁺R₁₁R₁₂R₁₃ or X—N⁺R₁₁R₁₂R₁₃, wherein X has thesame definition as above, and wherein g is 0 or 1;

Z is an optional polyethyleneoxy unit of formula (OCH₂CH₂)_(p), whereinp is 0 or an integer from 2 to about 1000, or F1-E1-P-E2-F2 unit inwhich E1 and E2 are the same or different and are C═O, O, or NR14,wherein R₁₄ is H, a linear alkyl having from 1-6 carbon atoms, abranched or cyclic alkyl having from 3 to 6 carbon atoms, a linear,branched or cyclic alkenyl or alkynyl having from 2 to 6 carbon atoms; Pis a peptide unit between 2 and 20 amino acids in length, wherein E1 orE2 can be linked to the peptide through the terminal nitrogen, terminalcarbon or through a side chain of one of the amino acids of the peptide;and F1 and F2 are the same or different and are an optionalpolyethyleneoxy unit of formula (OCH₂CH₂)_(p), wherein p is 0 or aninteger from 2 to about 1000, provided that when Z is not F1-E1-P-E2-F2,at least one of R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, and R₁₀ is a chargedsubstituent or when g is 1, at least one of A, R₁, R₂, R₃, R₄, R₅, R₆,R₇, R₈, R₉, and R₁₀ is a charged substituent;

Y represents a carbonyl, thioether, amide, disulfide, or hydrazonegroup; and q is an integer from 1 to 20.

As described in more detail below, the drug can be any of many smallmolecule drugs, including, but not limited to, maytansinoids, CC-1065analogs, morpholinos, doxorubicins, taxanes, cryptophycins, epothilones,calicheamicins, auristatins, and pyrrolobenzodiazepine dimers.

In preferred embodiments, one of R₁, R₂, R₃, R₄, R₉, R₁₀ is a chargedsubstituent selected from sulfonate, phosphate, carboxylate ortrialkylammonium, and the rest are H, l, g and m are each 0, n=1, D is amaytansinoid, a CC-1065 analog or a pyrrolobenzodiazepine dimer. Inanother more preferred embodiment, one of R₁, R₂, R₃, R₄, R₉, R₁₀ is asulfonate, and the rest are H, l, g and m are each 0, n=1, D is amaytansinoid, CC-1065 analog or a pyrrolobenzodiazepine dimer linked viaa disulfide, thioester, or thioether bond. In a further more preferredembodiment, one of R₁, R₂, R₃, R₄, R₉, R₁₀ is a sulfonate, and the restare H, l, g and m are each 0, n=1, and Q is a maytansinoid, a CC-1065analog, or a taxane.

In a preferred embodiment, when Z is an F1-E1-P-E2-F2 unit, E1 and E2are the same or different and are C═O or NR14, wherein R₁₄ is H, alinear alkyl having from 1-6 carbon atoms, a branched or cyclic alkylhaving from 3 to 6 carbon atoms, P is a peptide unit between 2 and 8amino acids in length, wherein E1 or E2 can be linked to the peptidethrough the terminal nitrogen, terminal carbon or through a side chainof one of the amino acids of the peptide, preferred amino acid residuesare glycine (gly), alanine (ala), leucine (leu), glutamic acid (glu), orlysine (lys), which can be used in any combination or any order (e.g.,gly-gly-gly or ala-leu-ala-leu, etc.); and F1 and F2 are the same ordifferent and are an optional polyethyleneoxy unit of formula(OCH₂CH₂)_(p), wherein p is 0 or an integer from 2 to about 1000.

In a more preferred embodiment, when Z is an F1-E1-P-E2-F2 unit, E1 andE2 are the same or different and are C═O or NR14, wherein R₁₄ is H or alinear alkyl having from 1-6 carbon atoms, P is a peptide unit between 2and 5 amino acids in length, wherein E1 or E2 can be linked to thepeptide through the terminal nitrogen, terminal carbon or through a sidechain of one of the amino acids of the peptide; and F1 and F2 are thesame or different and are an optional polyethyleneoxy unit of formula(OCH₂CH₂)_(p), wherein p is 0 or an integer from 2 to 24.

Preferably, q, the number of drugs bound to each cell-binding agent is1-20, more preferably 2-18, and even more preferably 2-16, and mostpreferably 2-10.

To synthesize the conjugate, the cell-binding agent can be modified withthe crosslinkers of the present invention to introduce reactivedisulfide groups, maleimido, haloacetyl or hydrazide groups. Synthesisof the cell-binding agent-drug conjugates linked via disulfide bonds isachieved by a disulfide exchange between the disulfide bond in themodified cell-binding agent and a drug containing a free thiol group.Synthesis of the cell-binding agent-drug conjugates linked via thioetheris achieved by reaction of the maleimido or haloacetyl modifiedcell-binding agent and a drug containing a free thiol group. Synthesisof conjugates bearing an acid labile hydrazone link can be achieved byreaction of a carbonyl group with the hydrazide moiety in the linker, bymethods known in the art (see, for example, P. Hamann et al.,BioConjugate Chem., 13; 40-46, 2002; B. Laguzza et al., J.Med. Chem.,32; 548-555, 1959; P. Trail et al., Cancer Res., 57; 100-105, 1997).

Alternatively, the drug can be modified with the crosslinkers of thepresent invention to give a modified drug of formula (IV) bearing afunctionality capable of reacting with a cell binding agent. For examplea thiol-containing drug can be reacted with the charged or pro-chargedcrosslinker of formula (I) bearing a maleimdo substituent at neutral pHin aqueous buffer to give a drug connected to the charged linker via athioether link. A thiol-containg drug can undergo disulfide exchangewith a charged linker bearing a pyrdiyldithio moiety to give a modifieddrug attached via a disulfide bond to the charged crosslinker. A drugbearing a hydroxyl group can be reacted with a charged or pro-chargedcrosslinker bearing a halogen, in the presence of a mild base, to give amodified drug bearing an ether link. A hydroxyl group containing drugcan be condensed with a charged crosslinker of formula (I) bearing acarboxyl group, in the presence of a dehydrating agent, such asdicyclohexylcarbodimide, to give an ester link. An amino groupcontaining drug can similarly undergo condensation with a carboxyl groupon the charged or pro-charged crosslinker of formula (I) to give anamide bond.

The conjugate may be purified by standard biochemical means, such as gelfiltration on a Sephadex G25 or Sephacryl S300 column, adsorptionchromatography, and ion exchange or by dialysis as previously described.In some cases (e.g. folic acid, melanocyte stimulating hormone, EGF etc)the cell-binding agent-drug conjugates can be purified by chromatographysuch as by HPLC, medium pressure column chromatography or ion exchange.

Modified Cell-Binding Agents

The cell-binding agent modified by reaction with crosslinkers of thepresent invention are preferably represented by the formula (III)

wherein the substituents are as described above for the charged orpro-charged linker and the cell-binding agent drug conjugate.

In preferred embodiments, one of R₁, R₂, R₃, R₄, R₉, R₁₀ is a chargedsubstituent selected from sulfonate, phosphate, carboxyl ortrialkylammonium, and the rest are H, l, g and m are each 0, n=1, Q is adisulfide substituent, a maleimido, haloacetyl group, or a N-hydroxysuccinimide ester, and Y is thioether, amide, or disulfide. In anothermore preferred embodiment, one of R₁, R₂, R₃, R₄, R₉, R₁₀ is asulfonate, and the rest are H, l, g and m are each 0, n=1, Q is adisulfide, maleimido or haloacetyl moiety, and Y is thioether, amide, ordisulfide. In a further more preferred embodiment, one of R₁, R₂, R₃,R₄, R₉, R₁₀ is a sulfonate, and the rest are H, l, g and m are each 0,n=1, Q is a pyridyldithio or nitropyridyldithio group, and Y isthioether, amide, or disulfide.

In a preferred embodiment, when Z is an F1-E1-P-E2-F2 unit, E1 and E2are the same or different and are C═O or NR14, wherein R₁₄ is H, alinear alkyl having from 1-6 carbon atoms, a branched or cyclic alkylhaving from 3 to 6 carbon atoms, P is a peptide unit between 2 and 8amino acids in length, wherein E1 or E2 can be linked to the peptidethrough the terminal nitrogen, terminal carbon or through a side chainof one of the amino acids of the peptide, preferred amino acid residuesare glycine (gly), alanine (ala), leucine (leu), glutamic acid (glu), orlysine (lys), which can be used in any combination or any order (e.g.,gly-gly-gly or ala-leu-ala-leu, etc.); and F1 and F2 are the same ordifferent and are an optional polyethyleneoxy unit of formula(OCH₂CH₂)_(p), wherein p is 0 or an integer from 2 to about 1000.

In a more preferred embodiment, when Z is an F1-E1-P-E2-F2 unit, E1 andE2 are the same or different and are C═O or NR14, wherein R₁₄ is H or alinear alkyl having from 1-6 carbon atoms, P is a peptide unit between 2and 5 amino acids in length, wherein E1 or E2 can be linked to thepeptide through the terminal nitrogen, terminal carbon or through a sidechain of one of the amino acids of the peptide; and F1 and F2 are thesame or different and are an optional polyethyleneoxy unit of formula(OCH₂CH₂)_(p), wherein p is 0 or an integer from 2 to 24.

The modified cell-binding agent can be prepared by reacting thecell-binding agent with the charged crosslinkers by methods known in theart for other crosslinkers (U.S. Pat. Nos. 6,340,701 B1, 5,846,545,5,585,499, 5,475,092, 5,414,064, 5,208,020, and 4,563,304; R. V. J.Chari et al. Cancer Research 52, 127-131, 1992; R. V. J. Chari et al.Cancer Research 55, 4079-4084, 1995; J. Carlsson et al. 173 Biochem. J.(1978) 723-737(1978); Goff, D. A., Carroll, S. F. 1 BioConjugate Chem.381-386 (1990); L. Delprino et al. 82 J. Pharm. Sci. 506-512 (1993); S.Arpicco et al., 8 BioConjugate Chem 327-337 (1997)). Advantageously,because the cross-linker groups are soluble in water or require only asmall percentage of organic solvent to maintain solubility in aqueoussolution, the reaction between the cell-binding agent and thecross-linker can be conducted in aqueous solution. The cross-linkingreagent is dissolved in aqueous buffer, optionally containing a smallamount (typically <10% by volume) of a polar organic solvent that ismiscible with water, for example different alcohols, such as methanol,ethanol, and propanol, dimethyl formamide, dimethyl acetamide, ordimethylsulfoxide at a high concentration, for example 1-100 mM, andthen an appropriate aliquot is added to the buffered aqueous solution ofthe cell-binding agent. An appropriate aliquot is an amount of solutionthat introduces 1-10 cross-linking groups per cell-binding agent,preferably 1-5 groups, and the volume to be added should not exceed 10%,preferably 5%, and most preferably 0-3% of the volume of thecell-binding agent solution. The aqueous solutions for the cell-bindingagents are buffered between pH 6 and 9, preferably between 6.5 and 7.5and can contain any non-nucleophilic buffer salts useful for these pHranges. Typical buffers include phosphate, triethanolamine.HCl, HEPES,and MOPS buffers, which can contain additional components, such assucrose and salts, for example, NaCl. After the addition the reaction isincubated at a temperature of from 4° C. to 40° C., preferably atambient temperature. The progress of the reaction can be monitored bymeasuring the increase in the absorption at 495 nm or anotherappropriate wavelength. After the reaction is complete, isolation of themodified cell-binding agent can be performed in a routine way, using forexample gel filtration chromatography, or adsorptive chromatography.

The extent of modification can be assessed by measuring the absorbanceof the nitropyridine thione, dinitropyridine dithione,carboxamidopyridine dithione or dicarboxamidopyridine dithione groupreleased. In a non limiting example, FIG. 56 shows the results from themodification of the cell-binding agent, the C242 antibody, with asulfonate crosslinker of the present invention. The time course oflinker/antibody (L/A) incorporation is shown, for example, along withthe drugs/antibody (D/A) linked. The charged or pro-charged crosslinkersdescribed herein have diverse functional groups that can react with anycell-binding agent that possesses a suitable substituent. For examplecell-binding agents bearing an amino or hydroxyl substituent can reactwith crosslinkers bearing an N-hydroxysuccinimide ester, cell-bindingagents bearing a thiol substituent can react with crosslinkers bearing amaleimido or haloacetyl group. Additionally, cell-binding agents bearinga carbonyl substituent can react with crosslinkers bearing a hydrazide.One skilled in the art can readily determine which crosslinker to usebased on the known reactivity of the available functional group on thecell-binding agent.

Crosslinkers bearing a positive charge (for example, compound 214, FIG.71) can be directly reacted with a cell binding agent in aqueous bufferat a pH between 5 and 9, optionally containing an organic cosolvent(such as 1 to 20% dimethylaceatmide or ethanol) to provide a modifiedcell binding agent bearing a positive charge and a thiol group. Thethiol group of the cell binding agent can be reacted with a cytotoxicdrug bearing either a maleimido, haloacetamido or an active disulfide(example pyridyldithio, nitropyridyldithio group) to provide aconjugate. The conjugate can be purified by the methods described above.

Alternatively, crosslinkers bearing a positive charge and a reactiveester (for example, compound 216, FIG. 71) can be directly reacted witha cell binding agent (for example, through its lysine amino group) tointroduce a positive charge and an active disulfide. Reaction with athiol-containing cytotoxic drug as described above can provide aconjugate bearing a positive charge.

Modified Cytotoxic Drugs

The cytotoxic drugs modified by reaction with crosslinkers of thepresent invention are preferably represented by the formula (IV):

wherein the substituents are as described above for the charged orpro-charged linker and the cell-binding agent drug conjugate.

In preferred embodiments, one of R₁, R₂, R₃, R₄, R₉, R₁₀ is a chargedsubstituent selected from sulfonate, phosphate, carboxyl ortrialkylammonium, and the rest are H, l, g and m are each 0, n=1, and Y′is a disulfide substituent, a maleimido, haloacetyl group, or aN-hydroxy succinimide ester. In another more preferred embodiment, oneof R₁, R₂, R₃, R₄, R₉, R₁₀ is a sulfonate, and the rest are H, l, g andm are each 0, n=1, and Y′ is a maleimido moiety or a N-hydroxysuccinimide ester. In a further more preferred embodiment, one of R₁,R₂, R₃, R₄, R₉, R₁₀ is a sulfonate, and the rest are H, l, g and m areeach 0, n=1, and Y′ is a N-hydroxy succinimide ester.

In a preferred embodiment, when Z is an F1-E1-P-E2-F2 unit, E1 and E2are the same or different and are C═O or NR14, wherein R₁₄ is H, alinear alkyl having from 1-6 carbon atoms, a branched or cyclic alkylhaving from 3 to 6 carbon atoms, P is a peptide unit between 2 and 8amino acids in length, wherein E1 or E2 can be linked to the peptidethrough the terminal nitrogen, terminal carbon or through a side chainof one of the amino acids of the peptide, preferred amino acid residuesare glycine (gly), alanine (ala), leucine (leu), glutamic acid (glu), orlysine (lys), which can be used in any combination or any order (e.g.,gly-gly-gly or ala-leu-ala-leu, etc.); and F1 and F2 are the same ordifferent and are an optional polyethyleneoxy unit of formula(OCH₂CH₂)_(p), wherein p is 0 or an integer from 2 to about 1000.

In a more preferred embodiment, when Z is an F1-E1-P-E2-F2 unit, E1 andE2 are the same or different and are C═O or NR14, wherein R₁₄ is H or alinear alkyl having from 1-6 carbon atoms, P is a peptide unit between 2and 5 amino acids in length, wherein E1 or E2 can be linked to thepeptide through the terminal nitrogen, terminal carbon or through a sidechain of one of the amino acids of the peptide; and F1 and F2 are thesame or different and are an optional polyethyleneoxy unit of formula(OCH₂CH₂)_(p), wherein p is 0 or an integer from 2 to 24.

The modified drugs can be prepared by reacting the drug with thecrosslinkers of the present invention to give a modified drug of formula(IV) bearing a functionality capable of reacting with a cell bindingagent. For example a thiol-containing drug can be reacted with thecharged or pro-charged crosslinker of formula (I) bearing a maleimdosubstituent at neutral pH in aqueous buffer to give a drug connected tothe charged or pro-charged linker via a thioether link. A thiol-containgdrug can undergo disulfide exchange with a charged or pro-charged linkerbearing a pyrdiyldithio moiety to give a modified drug attached via adisulfide bond to the charged or pro-charged crosslinker. A drug bearinga hydroxyl group can be reacted with a charged crosslinker bearing ahalogen, in the presence of a mild base, to give a modified drug bearingan ether link. A hydroxyl group containing drug can be condensed with acharged crosslinker of formula (I) bearing a carboxyl group, in thepresence of a dehydrating agent, such as dicyclohexylcarbodimide, togive an ester link. An amino group containing drug can similarly undergocondensation with a carboxyl group on the charged or pro-chargedcrosslinker of formula (I) to give an amide bond. The modified drug canbe purified by standard methods such as column chromatography oversilica gel or alumina, crystallization, preparatory thin layerchromatography, ion exchange chromatography or HPLC.

Cell-Binding Agents

The cell-binding agent that comprises the conjugates and the modifiedcell-binding agents of the present invention may be of any kindpresently known, or that become known, and includes peptides andnon-peptides. The cell-binding agent may be any compound that can bind acell, either in a specific or non-specific manner. Generally, these canbe antibodies (especially monoclonal antibodies and antibody fragments),adnectins (US Publication No.: 20070082365), interferons, lymphokines,hormones, growth factors, vitamins, nutrient-transport molecules (suchas transferrin), or any other cell-binding molecule or substance.

Where the cell-binding agent is an antibody (for example, a murine,human humanized, resurfaced or a chimeric or any other antibody known toone of skill in the art), it binds to an antigen that is a polypeptideand may be a transmembrane molecule (e.g. receptor) or a ligand such asa growth factor. Exemplary antigens include molecules such as renin; agrowth hormone, including human growth hormone and bovine growthhormone; growth hormone releasing factor; parathyroid hormone; thyroidstimulating hormone; lipoproteins; alpha-1-antitrypsin; insulin A-chain;insulin B-chain; proinsulin; follicle stimulating hormone; calcitonin;luteinizing hormone; glucagon; clotting factors such as factor vmc,factor IX, tissue factor (TF), and von Willebrands factor; anti-clottingfactors such as Protein C; atrial natriuretic factor; lung surfactant; aplasminogen activator, such as urokinase or human urine or tissue-typeplasminogen activator (t-PA); bombesin; thrombin; hemopoietic growthfactor; tumor necrosis factor-alpha and -beta; enkephalinase; RANTES(regulated on activation normally T-cell expressed and secreted); humanmacrophage inflammatory protein (MIP-1-alpha); a serum albumin, such ashuman serum albumin; Muellerian-inhibiting substance; relaxin A-chain;relaxin B-chain; prorelaxin; mouse gonadotropin-associated peptide; amicrobial protein, such as beta-lactamase; DNase; IgE; a cytotoxicT-lymphocyte associated antigen (CTLA), such as CTLA-4; inhibin;activin; vascular endothelial growth factor (VEGF); receptors forhormones or growth factors; protein A or D; rheumatoid factors; aneurotrophic factor such as bone-derived neurotrophic factor (BDNF),neurotrophin-3, -4, -5, or -6 (NT-3, NT4, NT-5, or NT-6), or a nervegrowth factor such as NGF-β; platelet-derived growth factor (PDGF);fibroblast growth factor such as aFGF and bFGF; epidermal growth factor(EGF); transforming growth factor (TGF) such as TGF-alpha and TGF-beta,including TGF-β1, TGF-β2, TGF-β3, TGF-β4, or TGF-β5; insulin-like growthfactor-I and -II (IGF-I and IGF-II); des(1-3)-IGF-I (brain IGF-I),insulin-like growth factor binding proteins, EpCAM, GD3, FLT3, PSMA,PSCA, MUC1, MUC16, STEAP, CEA, TENB2, EphA receptors, EphB receptors,folate receptor, mesothelin, cripto, alpha_(v)beta₆, integrins, VEGF,VEGFR, tarnsferrin receptor, IRTA1, IRTA2, IRTA3, IRTA4, IRTA5; CDproteins such as CD2, CD3, CD4, CD5, CD6, CD8, CD11, CD14, CD19, CD20,CD21, CD22, CD23, CD25, CD26, CD28, CD30, CD33, CD36, CD37, CD38, CD40,CD44, CD52, CD55, CD56, CD59, CD70, CD79, CD80, CD81, CD103, CD105,CD134, CD137, CD138, CD152 or an antibody which binds to one or moretumor-associated antigens or cell-surface receptors disclosed in USPublication No. 20080171040 or US Publication No. 20080305044 and areincorporated in their entirety by reference; erythropoietin;osteoinductive factors; immunotoxins; a bone morphogenetic protein(BMP); an interferon, such as interferon-alpha, -beta, and -gamma;colony stimulating factors (CSFs), e.g., M-CSF, GM-CSF, and G-CSF;interleukins (ILs), e.g., IL-1 to IL-10; superoxide dismutase; T-cellreceptors; surface membrane proteins; decay accelerating factor; viralantigen such as, for example, a portion of the HIV envelope; transportproteins; homing receptors; addressins; regulatory proteins; integrins,such as CD11a, CD11b, CD11c, CD18, an ICAM, VLA-4, EpCAM and VCAM; atumor associated antigen such as HER2, HER3 or HER4 receptor; andfragments of any of the above-listed polypeptides.

Preferred antigens for antibodies encompassed by the present inventionalso include CD proteins, such as CD3, CD4, CD8, CD19, CD20, CD34, andCD46; members of the ErbB receptor family, such as the EGF receptor,HER2, HER3 or HER4 receptor; cell adhesion molecules, such as LFA-1,Mac1, p150.95, VLA-4, ICAM-1, VCAM, EpCAM, alpha₄/beta₇ integrin, andalpha v/beta3 integrin including either alpha or beta subunits thereof(e.g. anti-CD11a, anti-CD18 or anti-CD11b antibodies); growth factors,such as VEGF; tissue factor (TF); TGF-β.; alpha interferon (alpha-IFN);an interleukin, such as IL-8; IgE; blood group antigens Apo2, deathreceptor; flk2/flt3 receptor; obesity (OB) receptor; mpl receptor;CTLA-4; protein C etc. Preferred antibodies that can be used areantibodies to CD2, CD3, CD4, CD5, CD6, CD11, CD19, CD20, CD22, CD26,CD30, CD33, CD37, CD38, CD40, CD44, CD56, CD79, CD105, CD138, EphAreceptors (e.g., EphA2 receptor), EphB receptors, EGFr, EGFRvIII, HER2,HER3, trastuzumab, pertuzumab mesothelin, cripto, alpha_(v)beta₆,integrins, VEGF, VEGFR, folate receptor (for example, FOLR1),transferrin receptor, GD3, EpCAM or an antibody which binds to one ormore tumor-associated antigens or cell-surface receptors disclosed in USPublication No. 20080171040 or US Publication No. 20080305044 and areincorporated in their entirety by reference.

Additional examples of cell-binding agents that can be used include:

-   -   resurfaced antibodies (U.S. Pat. No. 5,639,641);    -   humanized or fully human antibodies, selected from but not        limited to, huMy9-6, huB4, huC242, huN901, DS6, CD38, IGF-IR,        CNTO 95, B-B4, trastuzumab, pertuzumab, bivatuzumab,        sibrotuzumab, and rituximab (see, e.g., U.S. Pat. Nos.        5,639,641, 5,665,357; and 7,342,110, U.S. Provisional Patent        Application No. 60/424,332, International Patent Application WO        02/16,401, U.S. Patent Publication Number 20060045877, U.S.        Patent Publication Number 20060127407, U.S. Patent Publication        Number 20050118183, Pedersen et al., (1994) J. Mol. Biol. 235,        959-973, Roguska et al., (1994) Proceedings of the National        Academy of Sciences, Vol 91, 969-973, supra, Colomer et al.,        Cancer Invest., 19: 49-56 (2001), Heider et al., Eur. J. Cancer,        31A: 2385-2391 (1995), Welt et al., J. Clin. Oncol., 12:        1193-1203 (1994), and Maloney et al., Blood, 90: 2188-2195        (1997)); and    -   epitope-binding fragments of antibodies such as sFv, Fab, Fab′,        and F(ab′)₂ (Parham, J. Immunol. 131:2895-2902 (1983); Spring et        al, J. Immunol. 113:470-478 (1974); Nisonoff et al, Arch.        Biochem. Biophys. 89:230-244 (1960)).        Additional cell-binding agents include other cell-binding        proteins and polypeptides exemplified by, but not limited to:    -   Ankyrin repeat proteins (DARPins; Zahnd et al., J. Biol. Chem.,        281, 46, 35167-35175, (2006); Binz, H. K., Amstutz, P. &        Pluckthun, A. (2005) Nature Biotechnology, 23, 1257-1268) or        ankyrin-like repeats proteins or synthetic peptides described,        for example, in U.S. Patent Publication Number 20070238667; U.S.        Pat. No. 7,101,675; and WO/2007/147213; WO/2007/062466);    -   interferons (e.g. α, β, γ);    -   lymphokines such as IL-2, IL-3, IL-4, IL-6;    -   hormones such as insulin, TRH (thyrotropin releasing hormones),        MSH (melanocyte-stimulating hormone), steroid hormones, such as        androgens and estrogens;    -   vitamins such as folic acid;    -   growth factors and colony-stimulating factors such as EGF,        TGF-α, G-CSF, M-CSF and GM-CSF (Burgess, Immunology Today        5:155-158 (1984)); and    -   transferrin (O'Keefe et al, J. Biol. Chem. 260:932-937 (1985)).

Monoclonal antibody techniques allow for the production of specificcell-binding agents in the form of monoclonal antibodies. Particularlywell known in the art are techniques for creating monoclonal antibodiesproduced by immunizing mice, rats, hamsters or any other mammal with theantigen of interest such as the intact target cell, antigens isolatedfrom the target cell, whole virus, attenuated whole virus, and viralproteins such as viral coat proteins. Sensitized human cells can also beused. Another method of creating monoclonal antibodies is the use ofphage libraries of sFv (single chain variable region), specificallyhuman sFv (see, e.g., Griffiths et al, U.S. Pat. No. 5,885,793;McCafferty et al, WO 92/01047; and Liming et al, WO 99/06587.)

Selection of the appropriate cell-binding agent is a matter of choicethat depends upon the particular cell population that is to be targeted,but in general monoclonal antibodies and epitope binding fragmentsthereof are preferred, if an appropriate one is available.

For example, the monoclonal antibody My9 is a murine IgG_(2a) antibodythat is specific for the CD33 antigen found on Acute Myeloid Leukemia(AML) cells (Roy et al. Blood 77:2404-2412 (1991)) and can be used totreat AML patients. Similarly, the monoclonal antibody anti-B4 is amurine IgG₁, which binds to the CD19 antigen on B cells (Nadler et al,J. Immunol. 131:244-250 (1983)) and can be used if the target cells areB cells or diseased cells that express this antigen such as innon-Hodgkin's lymphoma or chronic lymphoblastic leukemia. Similarly, theantibody N901 is a murine monoclonal IgG₁ antibody that binds to CD56found on small cell lung carcinoma cells and on cells of other tumors ofthe neuroendocrine origin (Roy et al. J. Nat. Cancer Inst. 88:1136-1145(1996)), C242 antibody that binds to the CanAg antigen, pertuzumab,trastuzumab that binds to HER2/neu, and anti-EGF receptor antibody.

Additionally, GM-CSF, which binds to myeloid cells, can be used as acell-binding agent to diseased cells from acute myelogenous leukemia.IL-2, which binds to activated T-cells, can be used for prevention oftransplant graft rejection, for therapy and prevention ofgraft-versus-host disease, and for treatment of acute T-cell leukemia.MSH, which binds to melanocytes, can be used for the treatment ofmelanoma. Folic acid, which targets the folate receptor expressed onovarian and other cancers is also a suitable cell-binding agent.

Cancers of the breast and testes can be successfully targeted withestrogen (or estrogen analogues) or androgen (or androgen analogues),respectively, as cell-binding agents.

Drugs

Drugs that can be used in the present invention include chemotherapeuticagents. “Chemotherapeutic agent” is a chemical compound useful in thetreatment of cancer. Examples of chemotherapeutic agents includealkylating agents, such as thiotepa and cyclophosphamide (CYTOXAN™);alkyl sulfonates such as busulfan, improsulfan and piposulfan;aziridines, such as benzodopa, carboquone, meturedopa, and uredopa;ethylenimines and methylamelamines including altretamine,triethylenemelamine, trietylenephosphoramide,triethylenethiophosphaoramide and trimethylolomelamine; acetogenins(especially bullatacin and bullatacinone); a camptothecin (including thesynthetic analogue topotecan); bryostatin; callystatin; CC-1065(including its adozelesin, carzelesin and bizelesin syntheticanalogues); cryptophycins (particularly cryptophycin 1 and cryptophycin8); dolastatin; duocarmycin (including the synthetic analogues, KW-2189and CBI-TMI); eleutherobin; pancratistatin; a sarcodictyin;spongistatin; nitrogen mustards such as chlorambucil, chlornaphazine,cholophosphamide, estramustine, ifosfamide, mechlorethamine,mechlorethamine oxide hydrochloride, melphalan, novembichin,phenesterine, prednimustine, trofosfamide, uracil mustard; nitrosureassuch as carmustine, chlorozotocin, fotemustine, lomustine, nimustine,ranimustine; antibiotics, such as the enediyne antibiotics (e.g.calicheamicin, especially calicheamicin .gamma1 and calicheamicin thetaI, see, e.g., Angew Chem Intl. Ed. Engl. 33:183-186 (1994); dynemicin,including dynemicin A; an esperamicin; as well as neocarzinostatinchromophore and related chromoprotein enediyne antiobioticchromomophores), aclacinomysins, actinomycin, authramycin, azaserine,bleomycins, cactinomycin, carabicin, carminomycin, carzinophilin;chromomycins, dactinomycin, daunorubicin, detorubicin,6-diazo-5-oxo-L-norleucine, doxorubicin (includingmorpholino-doxorubicin, cyanomorpholino-doxorubicin,2-pyrrolino-doxorubicin and deoxydoxorubicin), epirubicin, esorubicin,idarubicin, marcellomycin, nitomycins, mycophenolic acid, nogalamycin,olivomycins, peplomycin, potfiromycin, puromycin, quelamycin,rodorubicin, streptonigrin, streptozocin, tubercidin, ubenimex,zinostatin, zorubicin; anti-metabolites, such as methotrexate and5-fluorouracil (5-FU); folic acid analogues, such as denopterin,methotrexate, pteropterin, trimetrexate; purine analogs, such asfludarabine, 6-mercaptopurine, thiamiprine, thioguanine; pyrimnidineanalogs such as, ancitabine, azacitidine, 6-azauridine, carmofur,cytarabine, dideoxyuridine, doxifluridine, enocitabine, floxuridine,5-FU; androgens, such as calusterone, dromostanolone propionate,epitiostanol, mepitiostane, testolactone; anti-adrenals, such asaminoglutethimide, mitotane, trilostane; folic acid replenisher, such asfrolinic acid; aceglatone; aldophosphamide glycoside; aminolevulinicacid; amsacrine; bestrabucil; bisantrene; edatraxate; defofamine;demecolcine; diaziquone; elfomithine; elliptinium acetate; anepothilone; etoglucid; gallium nitrate; hydroxyurea; lentinan;lonidamine; maytansinoids, such as maytansine and ansamitocins;mitoguazone; mitoxantrone; mopidamol; nitracrine; pentostatin; phenamet;pirarubicin; podophyllinic acid; 2-ethylhydrazide; procarbazine; PSK®;razoxane; rhizoxin; sizofiran; spirogermanium; tenuazonic acid;triaziquone; 2, 2′,2″-trichlorotriethylamine; trichothecenes (especiallyT-2 toxin, verracurin A, roridin A and anguidine); urethan; vindesine;dacarbazine; mannomustine; mitobronitol; mitolactol; pipobroman;gacytosine; arabinoside (“Ara-C”); cyclophosphamide; thiotepa; taxoids,e.g. paclitaxel (TAXOL®, Bristol-Myers Squibb Oncology, Princeton, N.J.)and doxetaxel (TAXOTERE®, Rhone-Poulenc Rorer, Antony, France);chlorambucil; gemcitabine; 6-thioguanine; mercaptopurine; methotrexate;platinum analogs such as cisplatin and carboplatin; vinblastine;platinum; etoposide (VP-16); ifosfamide; mitomycin C; mitoxantrone;vincristine; vinorelbine; navelbine; novantrone; teniposide; daunomycin;aminopterin; xeloda; ibandronate; CPT-11; topoisomerase inhibitor RFS2000; difluoromethylomithine (DMFO); retinoic acid; capecitabine; andpharmaceutically acceptable salts, acids or derivatives of any of theabove. Also included in this definition are anti-hormonal agents thatact to regulate or inhibit hormone action on tumors, such asanti-estrogens including for example tamoxifen, raloxifene, aromataseinhibiting 4(5)-imidazoles, 4-hydroxytamoxifen, trioxifene, keoxifene,LY117018, onapristone, and toremifene (Fareston); and anti-androgens,such as flutamide, nilutamide, bicalutamide, leuprolide, and goserelin;siRNA and pharmaceutically acceptable salts, acids or derivatives of anyof the above. Other chemotherapeutic agents that can be used with thepresent invention are disclosed in US Publication No. 20080171040 or USPublication No. 20080305044 and are incorporated in their entirety byreference.

In a preferred embodiment, chemotherapeutic drugs are essentially smallmolecule drugs. A “small molecule drug” is broadly used herein to referto an organic, inorganic, or organometallic compound that may have amolecular weight of for example 100 to 1500, more suitably from 120 to1200, favorably from 200 to 1000, and typically having a molecularweight of less than about 1000. Small molecule drugs of the inventionencompass oligopeptides and other biomolecules having a molecular weightof less than about 1000. Small molecule drugs are well characterized inthe art, such as in WO05058367A2, European Patent Application Nos.85901495 and 8590319, and in U.S. Pat. No. 4,956,303, among others andare incorporated in their entirety by reference.

Preferable small molecule drugs are those that allow for linkage to thecell-binding agent. The invention includes known drugs as well as thosethat may become known. Especially preferred small molecule drugs includecytotoxic agents.

The cytotoxic agent may be any compound that results in the death of acell, or induces cell death, or in some manner decreases cell viability,wherein each cytotoxic agent comprises a thiol moiety.

Preferred cytotoxic agents are maytansinoid compounds, taxane compounds,CC-1065 compounds, daunorubicin compounds and doxorubicin compounds,pyrrolobenzodiazepine dimers, calicheamicins. Auristatins and analoguesand derivatives thereof, some of which are described below.

Other cytotoxic agents, which are not necessarily small molecules, suchas siRNA, are also encompassed within the scope of the instantinvention. For example, siRNAs can be linked to the crosslinkers of thepresent invention by methods commonly used for the modification ofoligonucleotides (see, for example, US Patent Publications 20050107325and 20070213292). Thus the siRNA in its 3′ or 5′-phosphoromidite form isreacted with one end of the crosslinker bearing a hydroxyl functionalityto give an ester bond between the siRNA and the crosslinker. Similarlyreaction of the siRNA phosphoramidite with a crosslinker bearing aterminal amino group results in linkage of the crosslinker to the siRNAthrough an amine. siRNA are described in detail in U.S. PatentPublication Numbers: 20070275465, 20070213292, 20070185050, 20070161595,20070054279, 20060287260, 20060035254, 20060008822, 20050288244,20050176667, which are incorporated herein in their entirety byreference.

Maytansinoids

Maytansinoids that can be used in the present invention are well knownin the art and can be isolated from natural sources according to knownmethods or prepared synthetically according to known methods.

Examples of suitable maytansinoids include maytansinol and maytansinolanalogues. Examples of suitable maytansinol analogues include thosehaving a modified aromatic ring and those having modifications at otherpositions.

Specific examples of suitable analogues of maytansinol having a modifiedaromatic ring include:

(1) C-19-dechloro (U.S. Pat. No. 4,256,746) (prepared by LAH reductionof ansamitocin P2);

(2) C-20-hydroxy (or C-20-demethyl)+/−C-19-dechloro (U.S. Pat. Nos.4,361,650 and 4,307,016) (prepared by demethylation using Streptomycesor Actinomyces or dechlorination using LAH); and

(3) C-20-demethoxy, C-20-acyloxy (—OCOR), +/−dechloro (U.S. Pat. No.4,294,757) (prepared by acylation using acyl chlorides).

Specific examples of suitable analogues of maytansinol havingmodifications of other positions include:

(1)C-9-SH (U.S. Pat. No. 4,424,219) (prepared by the reaction ofmaytansinol with H2S or P2S5);

(2)C-14-alkoxymethyl (demethoxy/CH2OR) (U.S. Pat. No. 4,331,598);

(3)C-14-hydroxymethyl or acyloxymethyl (CH2OH or CH2OAc) (U.S. Pat. No.4,450,254) (prepared from Nocardia);

(4)C-15-hydroxy/acyloxy (U.S. Pat. No. 4,364,866) (prepared by theconversion of maytansinol by Streptomyces);

(5)C-15-methoxy (U.S. Pat. Nos. 4,313,946 and 4,315,929) (isolated fromTrewia nudiflora);

(6)C-18-N-demethyl (U.S. Pat. Nos. 4,362,663 and 4,322,348) (prepared bythe demethylation of maytansinol by Streptomyces); and

(7) 4,5-deoxy (U.S. Pat. No. 4,371,533) (prepared by the titaniumtrichloride/LAH reduction of maytansinol).

The synthesis of thiol-containing maytansinoids useful in the presentinvention is fully disclosed in U.S. Pat. Nos. 5,208,020, 5,416,064, andU. S. Patent Application No. 20040235840.

Maytansinoids with a thiol moiety at the C-3 position, the C-14position, the C-15 position or the C-20 position are all expected to beuseful. The C-3 position is preferred and the C-3 position ofmaytansinol is especially preferred. Also preferred are anN-methyl-alanine-containing C-3 thiol moiety maytansinoid, and anN-methyl-cysteine-containing C-3 thiol moiety maytansinoid, andanalogues of each.

Specific examples of N-methyl-alanine-containing C-3 thiol moietymaytansinoid derivatives useful in the present invention are representedby the formulae M1, M2, M3, M6 and M7.

wherein:

l is an integer of from 1 to 10; and

may is a maytansinoid.

wherein:

R₁ and R₂ are H, CH₃ or CH₂CH₃, and may be the same or different;

m is 0, 1, 2 or 3; and

may is a maytansinoid.

wherein:

n is an integer of from 3 to 8; and

may is a maytansinoid.

wherein:

l is 1, 2 or 3;

Y₀ is Cl or H; and

X₃ is H or CH₃.

wherein:

R₁, R₂, R₃, R₄ are H, CH₃ or CH₂CH₃, and may be the same or different;

m is 0, 1, 2 or 3; and

may is a maytansinoid.

Specific examples of N-methyl-cysteine-containing C-3 thiol moietymaytansinoid derivatives useful in the present invention are representedby the formulae M4 and M5.

wherein:

o is 1, 2 or 3;

p is an integer of 0 to 10; and

may is a maytansinoid.

wherein:

o is 1, 2 or 3;

q is an integer of from 0 to 10;

Y₀ is Cl or H; and

X₃ is H or CH₃.

Preferred maytansinoids are those described in U.S. Pat. Nos. 5,208,020;5,416,064; 6,333.410; 6,441,163; 6,716,821; RE39,151 and 7,276,497.

Taxanes

The cytotoxic agent according to the present invention may also be ataxane.

Taxanes that can be used in the present invention have been modified tocontain a thiol moiety. Some taxanes useful in the present inventionhave the formula T1 shown below:

Four embodiments of these novel taxanes are described below.

In embodiments (1), (2), (3), and (4), R₁, R₁′, and R₁″ are the same ordifferent and are H, an electron withdrawing group, such as F, NO₂, CN,Cl, CHF₂, or CF₃ or an electron donating group, such as —OCH₃, —OCH₂CH₃,—NR₇R₈, —OR₉, wherein R₇ and R₈ are the same or different and arelinear, branched, or cyclic alkyl groups having 1 to 10 carbon atoms orsimple or substituted aryl having 1 to 10 carbon atoms. Preferably thenumber of carbon atoms for R₇ and R₈ is 1 to 4. Also, preferably R₇ andR₈ are the same. Examples of preferred —NR₇R₈ groups include dimethylamino, diethyl amino, dipropyl amino, and dibutyl amino, where the butylmoiety is any of primary, secondary, tertiary or isobutyl. R₉ is linear,branched or cyclic alkyl having 1 to 10 carbon atoms.

R₁ preferably is OCH₃, F, NO₂, or CF₃.

Also preferably, R₁ is in the meta position and R₁′ and R₁″ are H orOCH₃.

R₂ in embodiments (1), (2) and (4), is H, heterocyclic, a linear,branched, or cyclic ester having from 1 to 10 carbon atoms orheterocyclic, a linear, branched, or cyclic ether having from 1 to 10carbon atoms or a carbamate of the formula —CONR₁₀R₁₁, wherein R₁₀ andR₁₁ are the same or different and are H, linear alkyl having from 1-6carbon atoms, branched, or cyclic alkyl having 3 to 10 atoms or simpleor substituted aryl having 6 to 10 carbon atoms. For esters, preferredexamples include —COCH₂CH₃ and —COCH₂CH₂CH₃. For ethers, preferredexamples include —CH₂CH₃ and —CH₂CH₂CH₃. For carbamates, preferredexamples include —CONHCH₂CH₃, —CONHCH₂CH₂CH₃, —CO-morpholine,—CO-piperazine, —CO-piperidino, or —CO—N-methylpiperazino.

R₂ in embodiment (3), is a thiol-containing moiety.

R₃ in embodiments (1), (3) and (4), is aryl, or is linear, branched orcyclic alkyl having 1 to 10 carbon atoms, preferably —CH₂CH(CH₃)₂.

R₃ in embodiment (2), is —CH═C(CH₃)₂.

R₄ in all four embodiments, is —OC(CH₃)₃ or —C₆H₅.

R₅ in embodiments (1) and (2), is a thiol-containing moiety and R₆ hasthe same definition as above for R₂ for embodiments (1), (2) and (4).

R₅ and R₆ in embodiment (3), are the same or different, and have thesame definition as above for R₂ for embodiments (1), (2) and (4).

R₅ in embodiment (4), has the same definition as above for R₂ forembodiments (1), (2) and (4) and R₆ is a thiol moiety.

The preferred positions for introduction of the thiol-containing moietyare R₂ and R₅, with R₂ being the most preferred.

The side chain carrying the thiol moiety can be linear or branched,aromatic or heterocyclic. One of ordinary skill in the art can readilyidentify suitable side chains. Specific examples of thiol moietiesinclude —(CH₂)_(n)SH, —CO(CH₂)_(n)SH, —(CH₂)_(n)CH(CH₃)SH,—CO(CH₂)_(n)CH(CH₃)SH, —(CH₂)nC(CH₃)₂SH, —CO(CH₂)_(n)C(CH₃)₂SH,—CONR₁₂(CH₂)_(n)SH, —CONR₁₂(CH₂)_(n)CH(CH₃)SH, or—CONR₁₂(CH₂)_(n)C(CH₃)₂SH, —CO-morpholino-XSH, —CO-piperazino-XSH,—CO-piperidino-XSH, and —CO—N-methylpiperazino-XSH wherein

X is a linear alkyl or branched alkyl having 1-10 carbon atoms.

R₁₂ is a linear alkyl, branched alkyl or cyclic alkyl having 1 to 10carbon atoms, or simple or substituted aryl having from 1 to 10 carbonatoms or heterocyclic, and can be H, and

n is an integer of 0 to 10.

Examples of linear alkyls include methyl, ethyl, propyl, butyl, pentyland hexyl.

Examples of branched alkyls include isopropyl, isobutyl, sec.-butyl,tert.-butyl, isopentyl and 1-ethyl-propyl.

Examples of cyclic alkyls include cyclopropyl, cyclobutyl, cyclopentyland cyclohexyl.

Examples of simple aryls include phenyl and naphthyl.

Examples of substituted aryls include aryls such as those describedabove substituted with alkyl groups, with halogens, such as Cl, Br, F,nitro groups, amino groups, sulfonic acid groups, carboxylic acidgroups, hydroxy groups or alkoxy groups.

Examples of heterocyclics are compounds wherein the heteroatoms areselected from O, N, and S, and include morpholino, piperidino,piperazino, N-methylpiperazino, pyrrollyl, pyridyl, furyl and thiophene.

The taxanes having a thiol moiety can be synthesized according to knownmethods. The starting material for the synthesis is the commerciallyavailable 10-deacetylbaccatin III. The chemistry to introduce varioussubstituents is described in several publications (Ojima et al, J. Med.Chem. 39:3889-3896 (1996); Ojima et al., J. Med. Chem. 40:267-278(1997); Ojima et al., Proc. Natl. Acad. Sci., 96:4256-4261 (1999); U.S.Pat. Nos. 5,475,011 and 5,811,452).

The substituent R₁ on the phenyl ring and the position of thesubstituent R₁ can be varied until a compound of the desired toxicity isobtained. Furthermore, the degree of substitution on the phenyl ring canbe varied to achieve a desired toxicity. That is, the phenyl ring canhave one or more substituents (e.g., mono-, di-, or tri-substitution ofthe phenyl ring) which provide another means for achieving a desiredtoxicity. One of ordinary skill in the art can determine the appropriatechemical moiety for R₁ and the appropriate position for R₁ using onlyroutine experimentation.

For example, electron withdrawing groups at the meta position increasethe cytotoxic potency, while substitution at the para position is notexpected to increase the potency as compared to the parent taxane.Typically, a few representative taxanes with substituents at thedifferent positions (ortho, meta and para) will be initially preparedand evaluated for in vitro cytotoxicity.

The thiol moiety can be introduced at one of the positions where ahydroxyl group already exists. The chemistry to protect the varioushydroxyl groups, while reacting the desired one, has been describedpreviously (see, for example, the references cited supra). Thesubstituent is introduced by simply converting the free hydroxyl groupto a disulfide-containing ether, a disulfide-containing ester, or adisulfide-containing carbamate. This transformation is achieved asfollows. The desired hydroxyl group is deprotonated by treatment withthe commercially-available reagent lithium hexamethyldisilazane (1.2equivalents) in tetrahydrofuran at −40° C. as described in Ojima et al.(1999), supra. The resulting alkoxide anion is then reacted with anexcess of a dihalo compound, such as dibromoethane, to give a haloether. Displacement of the halogen with a thiol (by reaction withpotassium thioacetate and treatment with mild base or hydroxylamine)will provide the desired thiol-containing taxane.

Alternatively, the desired hydroxyl group can be esterified directly byreaction with an acyl halide, such as 3-bromopropionyl chloride, to givea bromo ester. Displacement of the bromo group by treatment withpotassium thioacetate and further processing as described above willprovide the thiol-containing taxane ester. Preferred taxoids are thosedescribed in U.S. Pat. Nos. 6,340,701; 6,372,738; 6,436,931; 6,596,757;6,706,708; 7,008,942; 7,217,819 and 7,276,499.

CC-1065 Analogues

The cytotoxic agent according to the present invention may also be aCC-1065 analogue.

According to the present invention, the CC-1065 analogues contain an Asubunit and a B or a B-C subunit. The A subunits are CPI(cyclopropapyrroloindole unit) in its natural closed cyclopropyl form orin its open chloromethyl form, or the closely related CBI unit(cyclopropylbenzindole unit) in the closed cyclopropyl form or the openchloromethyl form. The B and C subunits of CC-1065 analogues are verysimilar and are 2-carboxy-indole and 2-carboxy-benzofuran derivatives.For activity, the analogues of CC-1065 need at least one such2-carboxy-indole subunit or 2-carboxy-benzofuran subunit, although twosubunits (i.e., B-C) render the analogue more potent. As is obvious fromthe natural CC-1065 and from the analogues published (e.g., Warpehoskiet al, J. Med. Chem. 31:590-603 (1988), D. Boger et al., J. Org. Chem;66; 6654-6661, 2001; U.S. Pat. Nos. 5,739,350; 6,060,608; 6.310.209),the B and C subunits can also carry different substituents at differentpositions on the indole or benzofuran rings.

CC-1065 analogues containing a thiol moiety can be any of the followingA subunits of the formulae A-1 {CPI (Cyclopropyl form)}, A-2 {CPI(Chloromethyl form)}, A-3 {CBI (Cyclopropyl form)}, and A-4 {CBI(Chloromethyl form)} covalently linked via an amide bond from thesecondary amino group of the pyrrole moiety of the A subunit to the C-2carboxy group of either a B subunit of the formula F-1 or a B-C subunitof the formulae F-3 or F-7.

A Subunits

B and Covalently Bound B and C Subunits

wherein each W₁ and W₂ may be the same or different and may be 0 or NH;and

wherein, in Formula F-1 R₄ is a thiol moiety, in Formula F-3 one of R orR₄ is a thiol moiety, in Formula F-7 one of R′ or R₄ is athiol-containing moiety; when R or R′ is a thiol moiety, then R₁ to R₆,which may be the same or different, are hydrogen, C₁-C₃ linear alkyl,methoxy, hydroxyl, primary amino, secondary amino, tertiary amino, oramido; and when R₄ is a thiol moiety, R, R₁, R₂, R₃, R₄, R₅ and R₆,which may be the same or different, are hydrogen, C₁-C₃ linear alkyl,methoxy, hydroxyl, primary amino, secondary amino, tertiary amino, oramido, and R′ is NH₂, alkyl, O-alkyl, primary amino, secondary amino,tertiary amino, or amido. In addition, the chlorine atom in A-2 and A-4subunits can be replaced with another suitable halogen.

In a preferred embodiment, R and R′ are thiol moieties and R₁ and R₂ areeach hydrogen. In another preferred embodiment, R and R′ are thiolmoieties and R₁ to R₆ are each hydrogen.

In an especially preferred embodiment, R or R₄ is —NHCO(CH₂)_(l)SH,—NHCOC₆H₄(CH₂)_(l)SH, or —O(CH₂)_(l)SH, and R′ is —(CH₂)_(l)SH,—NH(CH₂)_(l)SH or —O(CH₂)_(l)SH wherein l is an integer of 1 to 10.

Examples of primary amines include methyl amine, ethyl amine andisopropyl amine.

Examples of secondary amines include dimethyl amine, diethylamine andethylpropyl amine.

Examples of tertiary amines include trimethyl amine, triethyl amine, andethyl-isopropyl-methyl amine.

Examples of amido groups include N-methylacetamido,N-methyl-propionamido, N-acetamido, and N-propionamido.

Examples of alkyl represented by R′, when R′ is not a linking group,include C₁-C₅ linear or branched alkyl.

Examples of O-alkyl represented by R′ when R′ is not a linking group,include compounds where the alkyl moiety is a C₁-C₅ linear or branchedalkyl.

The above-described CC-1065 analogues may be isolated from naturalsources and methods for their preparation, involving subsequentmodification, synthetic preparation, or a combination of both, arewell-described (see, e.g., U.S. Pat. Nos. 5,475,092, 5,585,499 and5,846,545). Preferred CC-1065 analogs are those described in U.S. Pat.Nos. 5,475,092; 5,595,499; 5,846,545; 6,534,660; 6,586,618; 6,756,397and 7,049,316

Daunorubicin/Doxorubicin Analogues

The cytotoxic agent according to the present invention may also be adaunorubicin analogue or a doxorubicin analogue.

The daunorubicin and doxorubicin analogues of the present invention canbe modified to comprise a thiol moiety.

The modified doxorubicin/daunorubicin analogues useful in the presentinvention have the formula D1 shown below:

wherein,

X is H or OH;

Y is O or NR₂, wherein R₂ is linear or branched alkyl having 1 to 5carbon atoms;

R is a thiol moiety, H, or liner or branched alkyl having 1 to 5 carbonatoms; and

R′ is a thiol moiety, H, or —OR₁, wherein R₁ is linear or branched alkylhaving 1 to 5 carbon atoms;

provided that R and R′ are not thiol moieties at the same time.

In a preferred embodiment, NR₂ is NCH₃. In another preferred embodiment,R′ is —O.

In an especially preferred embodiment, the thiol moiety is —(CH₂)_(n)SH,—O(CH₂)_(n)SH, —(CH₂)_(n)CH(CH₃)SH, —O(CH₂)_(n)CH(CH₃)SH,—(CH₂)_(n)C(CH₃)₂SH, or —O(CH₂)_(n)C(CH₃)₂SH, wherein n is an integer of0 to 10.

Examples of the linear or branched alkyl having 1 to 5 carbon atoms,represented by R, R₁, and R₂, include methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, sec.-butyl, tert.-butyl, and pentyl, inany of its eight isomeric arrangements.

R₁ and R₂ preferably are methyl.

Examples of linear alkyls include methyl, ethyl, propyl, butyl, pentyland hexyl.

Examples of branched alkyls include isopropyl, isobutyl, sec.-butyl,tert.-butyl, isopentyl and 1-ethyl-propyl.

When either R or R′ is not a linking group, the substituent in thatposition can be varied until a compound of the desired toxicity isobtained. High toxicity is defined as having an IC₅₀ towards culturedcancer cells in the range of 1×10⁻¹² to 1×10⁻⁹ M, upon a 72 hourexposure time. Representative examples of substituents are H, alkyl, andO-alkyl, as described above. One of ordinary skill in the art candetermine the appropriate chemical moiety for R and R′ using onlyroutine experimentation.

For example, methyl and methoxy substituents are expected to increasethe cytotoxic potency, while a hydrogen is not expected to increase thepotency as compared to the parent daunorubicin analogues withsubstituents at the different positions will be initially prepared andevaluated for in vitro cytotoxicity.

The modified doxorubicin/daunorubicin analogues of the presentinvention, which have a thiol moiety, are described in WO 01/38318. Themodified doxorubicin/daunorubicin analogues can be synthesized accordingto known methods (see, e.g., U.S. Pat. No. 5,146,064).

Auristatin include auristatin E, auristatin EB (AEB), auristatin EFP(AEFP), monomethyl auristatin E (MMAE) and are described in U.S. Pat.No. 5,635,483, Int. J. Oncol. 15:367-72 (1999); Molecular CancerTherapeutics, vol. 3, No. 8, pp. 921-932 (2004); U.S. application Ser.No. 11/134,826. U.S. Patent Publication Nos. 20060074008, 2006022925.

The cytotoxic agents according to the present invention includepyrrolobenzodiazepine dimers that are known in the art (U.S. Pat. Nos.7,049,311; 7.067.511; 6,951,853; 7,189,710; 6,884,799; 6,660,856.

Analogues and Derivatives

One skilled in the art of cytotoxic agents will readily understand thateach of the cytotoxic agents described herein can be modified in such amanner that the resulting compound still retains the specificity and/oractivity of the starting compound. The skilled artisan will alsounderstand that many of these compounds can be used in place of thecytotoxic agents described herein. Thus, the cytotoxic agents of thepresent invention include analogues and derivatives of the compoundsdescribed herein.

Therapeutic Use

The cell-binding agent drug conjugates (e.g., immunoconjugates) of thisinvention can also be used in combination with other chemotherapeuticagents. Such chemotherapeutic agents are listed above or are describedin U.S. Pat. No. 7,303,749.

The cell-binding agent drug conjugates (e.g., immunoconjugates) of thepresent invention can be administered in vitro, in vivo and/or ex vivoto treat patients and/or to modulate the growth of selected cellpopulations including, for example, cancer of the lung, blood, plasma,breast, colon, prostate, kidney, pancreas, brain, bones, ovary, testes,and lymphatic organs; autoimmune diseases, such as systemic lupus,rheumatoid arthritis, and multiple sclerosis; graft rejections, such asrenal transplant rejection, liver transplant rejection, lung transplantrejection, cardiac transplant rejection, and bone marrow transplantrejection; graft versus host disease; viral infections, such as CMVinfection, HIV infection, and AIDS; and parasite infections, such asgiardiasis, amoebiasis, schistosomiasis, and the like. Preferably, theimmunoconjugates and chemotherapeutic agents of the invention areadministered in vitro, in vivo and/or ex vivo to treat cancer in apatient and/or to modulate the growth of cancer cells, including, forexample, cancer of the blood, plasma, lung, breast, colon, prostate,kidney, pancreas, brain, bones, ovary, testes, and lymphatic organs;more preferably lung, colon prostrate, plasma, blood or colon cancer.

“Modulating the growth of selected cell populations” includes inhibitingthe proliferation of selected cell populations (e.g., multiple myelomacell populations, such as MOLP-8 cells, OPM2 cells, H929 cells, and thelike) from dividing to produce more cells; reducing the rate of increasein cell division as compared, for example, to untreated cells; killingselected cell populations; and/or preventing selected cell populations(such as cancer cells) from metastasizing. The growth of selected cellpopulations can be modulated in vitro, in vivo or ex vivo.

In the methods of the present invention, the cell-binding agent drugconjugates (e.g., immunoconjugates) can be administered in vitro, invivo, or ex vivo. The cell-binding agent drug conjugates (e.g.,immunoconjugates) can be used with suitable pharmaceutically acceptablecarriers, diluents, and/or excipients, which are well known, and can bedetermined, by one of skill in the art as the clinical situationwarrants. Examples of suitable carriers, diluents and/or excipientsinclude: (1) Dulbecco's phosphate buffered saline, pH about 6.5, whichwould contain about 1 mg/ml to 25 mg/ml human serum albumin, (2) 0.9%saline (0.9% w/v NaCl), and (3) 5% (w/v) dextrose.

The compounds and compositions described herein may be administered inappropriate form, preferably parenterally, more preferablyintravenously. For parenteral administration, the compounds orcompositions can be aqueous or nonaqueous sterile solutions, suspensionsor emulsions. Propylene glycol, vegetable oils and injectable organicesters, such as ethyl oleate, can be used as the solvent or vehicle. Thecompositions can also contain adjuvants, emulsifiers or dispersants.

The compositions can also be in the form of sterile solid compositionsthat can be dissolved or dispersed in sterile water or any otherinjectable sterile medium.

The “therapeutically effective amount” of the cell-binding agent drugconjugate (e.g., immunoconjugates) described herein refers to the dosageregimen for modulating the growth of selected cell populations and/ortreating a patient's disease, and is selected in accordance with avariety of factors, including the age, weight, sex, diet and medicalcondition of the patient, the severity of the disease, the route ofadministration, and pharmacological considerations, such as theactivity, efficacy, pharmacokinetic and toxicology profiles of theparticular compound used. The “therapeutically effective amount” canalso be determined by reference to standard medical texts, such as thePhysicians Desk Reference 2004. The patient is preferably an animal,more preferably a mammal, most preferably a human. The patient can bemale or female, and can be an infant, child or adult.

Examples of suitable protocols of cell-binding agent drug conjugates(e.g., immunoconjugate) administration are as follows. The conjugatescan be given daily for about 5 days either as an i.v., bolus each dayfor about 5 days, or as a continuous infusion for about 5 days.

Alternatively, the conjugates can be administered once a week for sixweeks or longer. As another alternative, the conjugates can beadministered once every two or three weeks. Bolus doses are given inabout 50 to about 400 ml of normal saline to which about 5 to about 10ml of human serum albumin can be added. Continuous infusions are givenin about 250 to about 500 ml of normal saline, to which about 25 toabout 50 ml of human serum albumin can be added, per 24 hour period.Dosages will be about 10 pg to about 1000 mg/kg per person, i.v. (rangeof about 100 ng to about 100 mg/kg).

About one to about four weeks after treatment, the patient can receive asecond course of treatment. Specific clinical protocols with regard toroute of administration, excipients, diluents, dosages, and times can bedetermined by the skilled artisan as the clinical situation warrants.

The present invention also provides pharmaceutical kits comprising oneor more containers filled with one or more of the ingredients of thepharmaceutical compounds and/or compositions of the present invention,including, one or more immunoconjugates and one or more chemotherapeuticagents. Such kits can also include, for example, other compounds and/orcompositions, a device(s) for administering the compounds and/orcompositions, and written instructions in a form prescribed by agovernmental agency regulating the manufacture, use or sale ofpharmaceuticals or biological products.

The compounds and conjugates (e.g., immunoconjugates could also be usedfor the manufacture of a medicament useful for treating or lessening theseverity of disorders, such as, characterized by abnormal growth ofcells (e.g., cancer).

Cancer therapies and their dosages, routes of administration andrecommended usage are known in the art and have been described in suchliterature as the Physician's Desk Reference (PDR). The PDR disclosesdosages of the agents that have been used in treatment of variouscancers. The dosing regimen and dosages of these aforementionedchemotherapeutic agents and conjugates that are therapeuticallyeffective will depend on the particular cancer being treated, the extentof the disease and other factors familiar to the physician of skill inthe art and can be determined by the physician. For example, the 2006edition of the Physician's Desk Reference discloses that Taxotere (seep. 2947) is an inhibitor of tubulin depolymerization; Doxorubicin (see p786), Doxil (see p 3302) and oxaliplatin (see p 2908) are DNAinteracting agents, Irinotecal (see p. 2602) is a Topoisomerase Iinhibitor, Erbitux (see p 937) and Tarceva (see p 2470) interact withthe epidermal growth factor receptor. The contents of the PDR areexpressly incorporated herein in their entirety by reference. One ofskill in the art can review the PDR, using one or more of the followingparameters, to determine dosing regimens and dosages of thechemotherapeutic agents and conjugates, which can be used in accordancewith the teachings of this invention. These parameters include:

1. Comprehensive index

-   -   a) by Manufacturer    -   b) Products (by company's or trademarked drug name)    -   c) Category index (for example, “antihistamines”, “DNA        alkylating agents” taxanes etc.)    -   d) Generic/chemical index (non-trademark common drug names)

2. Color images of medications

3. Product information, consistent with FDA labeling

a) Chemical information

b) Function/action

c) Indications & Contraindications

d) Trial research, side effects, warnings

All references cited herein and in the examples that follow areexpressly incorporated by reference in their entireties.

EXAMPLES

The invention will now be described by reference to non-limitingexamples. Unless otherwise specified, all percents and ratios are byvolume.

Example 1: Materials and Methods Methyl 2-(acetylthio)-4-bromobutanoate

10.0 g (38.4 mmol) of methyl 2,4-dibromobutanoate in 100 ml of dry THFat 20° C. was added drop wise the mixture of 2.75 ml (38.5 mmol) ofthiolacetic acid in 8.5 ml (48.9 mmol) of DIPEA and 50 ml of dry THF in1.5 hour. After stirring overnight at −20° C. then 0° C. for 2 hoursunder Ar, the mixture was concentrated, diluted with EtAc/Hexane, washedwith 1.0 M NaH₂PO₄, dried over MgSO₄, filtered, evaporated, and SiO₂chromatographic purification (1:12 to 1:10 EtAc/Hexane) to afford 9.5 g(96%) of the title compound. 1H NMR (CDCl3) 4.38 (1H, t, J=7.1 Hz), 3.74(s, 3H), 3.40 (m, 2H), 2.57˜2.47 (m, 1H), 2.37 (s, 3H), 2.36˜2.21 (m,1H); 13C NMR 193.24, 171.36, 53.15, 44.45, 34.67, 30.46, 29.46; MSm/z+276.9 (M+Na), 278.9 (M+2+Na).

4-Bromo-1-methoxy-1-oxobutane-2-sulfonic Acid

9.2 g (36.3 mmol) of methyl 2-(acetylthio)-4-bromobutanoate in 80 ml ofacetic acid was added 40 ml of hydrogen peroxide (35% in water). Themixture was stirred overnight, then evaporated, diluted with water,neutralized with NaHCO₃, washed with 1:1 Hexane/EtAc. The aqueoussolution was evaporated, dissolved in methanol, concentrated, andcrystallized with methanol/toluene to afford 8.6 g (90% yield) of thetitle compound. m.p.=288˜293 (decomp); 1H NMR (D2O) 4.12 (dd, 1H, J=4.8,9.3 Hz), 3.83 (s, 3H), 3.64 (m, 1H), 3.53 (m, 1H), 2.54 (m, 2H); 13C NMR172.16, 66.73, 55.66, 33.39, 32.70; MS m/z− 260.8 (M−1).

4-(Acetylthio)-1-methoxy-1-oxobutane-2-sulfonic Acid

5.0 g (19.2 mmol) of 4-bromo-1-methoxy-1-oxobutane-2-sulfonic acid in100 ml of THF was added 3.0 ml of thioacetic acid and 9.0 ml of DIPEA in100 ml of THF. The mixture was stirred overnight then refluxed at 70° C.for 1 hr, evaporated and co-evaporated with 3×100 ml of water afterbeing neutralized to pH 7 with NaHCO₃. The mixture was redissolved inmethanol, filtered through celite, concentrated and purified with SiO₂chromatography eluted with CH₃OH/CH₂Cl₂/HCOOH 37.5:250:1 to 50:250:1) toafford 4.4 g (90% yield) of the title compound. 1H NMR (D2O) 3.95 (dd,1H, J=4.1, 10.3 Hz), 3.83 (s, 3H), 3.74 (m, 2H), 3.22 (dd, 2H, J=7.4,14.9 Hz), 2.39 (s, 3H); 13C NMR 203.88, 172.91, 67.32, 56.17, 29.04,20.61; MS m/z− 254.8 (M−H).

4-((5-nitropyridin-2-yl)disulfanyl)-2-sulfobutanoic Acid

3.0 g (11.7 mmol) of 4-(Acetylthio)-1-methoxy-1-oxobutane-2-sulfonicacid in 100 ml of water was added 50 ml of 3 M NaOH. After being stirredunder Ar for 3 h, the mixture was neutralized with 1 M H₂PO₄ to pH 7.2under Ar. The mixture was added dropwise to the solution of 10.0 g (32.2mmol) of 1,2-bis(5-nitropyridin-2-yl)disulfane in 200 ml of DMA. Afterbeing stirred for 4 h under Ar, the mixture was concentrated, dilutedwith water, filtered, evaporated and purified with C-18 4.0×20 cm columneluted with water/methanol (95:5) to afford 3.1 g (75% yield) of thetitle compound. m.p.=288˜291° C. (decomp.) 1H NMR (DMF-d7) 9.29 (d, 1H,J=2.2 Hz), 8.63 (dd, 1H, J=2.7, 8.9 Hz), 8.17 (d, 1H, J=8.9 Hz), 3.73(t, 1H, J=7.2 Hz), 3.22˜3.17 (m, 1H), 3.15˜3.10 (m, 1H), 2.41˜2.33 (m,2H); 13C NMR 170.92, 169.10, 146.04, 143.67, 133.65, 120.72, 64.22,37.82, 29.26; MS m/z− 352.8 (M−H).

1-(2,5-dioxopyrrolidin-1-yloxy)-4-((5-nitropyridin-2-yl)disulfanyl)-1-oxobutane-2-sulfonicAcid

220 mg (0.62 mmol) of4-((5-nitropyridin-2-yl)disulfanyl)-2-sulfobutanoic acid in 15 DMA wasadded 130 mg (1.13 mmol) of NHS and 480 mg (2.50 mmol) of EDC. Themixture was stirred under Ar overnight, evaporated and purified on SiO₂chromatography eluted with CH₂CH₂/CH₃OH/HCOOH (10000:1000:1 to10000:1500:1) to afford 227 mg (82% yield) of the title compound. 1H NMR(DMSO-d6) 9.25 (d, 1H, J=5.2 Hz), 8.57 (dd, 1H, J=2.5, 8.9 Hz), 8.04 (t,1H, J=8.0+8.9 Hz), 3.86 (dd, 1H, J=4.9, 9.7 Hz), 3.13-3.12 (m, 2H), 2.76(s, 4H), 2.36-2.30 (m, 1H), 2.25-2.21 (m, 1H); 13C NMR 166.96, 165.01,144.93, 142.26, 132.63, 119.61, 61.00, 35.03, 29.30, 25.39; MS m/z−449.8 (M−H).

Methyl 2-(acetylthio)-4-bromobutanoate

10.0 g (38.4 mmol) of methyl 2,4-dibromobutanoate in 100 ml of dry THFat −20° C. was added dropwise the mixture of 2.75 ml (38.5 mmol) ofthiolacetic acid in 8.5 ml (48.9 mmol) of DIPEA and 50 ml of dry THF in1.5 hour. After stirring overnight at −20° C. then 0° C. for 2 hoursunder Ar, the mixture was concentrated, diluted with EtAc/Hexane, washedwith 1.0 M NaH₂PO₄, dried over MgSO₄, filtered, evaporated, and SiO2chromatographic purification (1:12 to 1:10 EtAc/Hexane) to afford 9.5 g(96%) of the title compound. 1H NMR (CDCl3) 4.38 (1H, t, J=7.1 Hz), 3.74(s, 3H), 3.40 (m, 2H), 2.57˜2.47 (m, 1H), 2.37 (s, 3H), 2.36˜2.21 (m,1H); 13C NMR 193.24, 171.36, 53.15, 44.45, 34.67, 30.46, 29.46; MSm/z+276.9 (M+Na), 278.9 (M+2+Na).

4-Bromo-1-methoxy-1-oxobutane-2-sulfonic Acid

9.2 g (36.3 mmol) of methyl 2-(acetylthio)-4-bromobutanoate in 80 ml ofacetic acid was added 40 ml of hydrogen peroxide (35% in water). Themixture was stirred overnight, then evaporated, diluted with water,neutralized with NaHCO₃, washed with 1:1 Hexane/EtAc. The aqueoussolution was evaporated, dissolved in methanol, concentrated, andcrystallized with methanol/toluene to afford 8.6 g (90% yield) of thetitle compound. m.p.=288˜293 (decomp); 1H NMR (D2O) 4.12 (dd, 1H, J=4.8,9.3 Hz), 3.83 (s, 3H), 3.64 (m, 1H), 3.53 (m, 1H), 2.54 (m, 2H); 13C NMR172.16, 66.73, 55.66, 33.39, 32.70; MS m/z− 260.8 (M-1).

4-(Acetylthio)-1-methoxy-1-oxobutane-2-sulfonic Acid

5.0 g (19.2 mmol) of 4-bromo-1-methoxy-1-oxobutane-2-sulfonic acid in100 ml of THF was added 3.0 ml of thioacetic acid and 9.0 ml of DIPEA in100 ml of THF. The mixture was stirred overnight then refluxed at 70° C.for 1 hr, evaporated and co-evaporated with 3×100 ml of water afterneutralized to pH 7 with NaHCO₃. The mixture was redissolved inmethanol, filtered through celite, concentrated and purified with SiO₂chromatography eluted with CH₃OH/CH₂Cl₂/HCOOH 37.5:250:1 to 50:250:1) toafford 4.4 g (90% yield) of the title compound. 1H NMR (D2O) 3.95 (dd,1H, J=4.1, 10.3 Hz), 3.83 (s, 3H), 3.74 (m, 2H), 3.22 (dd, 2H, J=7.4,14.9 Hz), 2.39 (s, 3H); 13C NMR 203.88, 172.91, 67.32, 56.17, 29.04,20.61; MS m/z− 254.8 (M−H).

4-((5-nitropyridin-2-yl)disulfanyl)-2-sulfobutanoic Acid

3.0 g (11.7 mmol) of 4-(Acetylthio)-1-methoxy-1-oxobutane-2-sulfonicacid in 100 ml of water was added 50 ml of 3 M NaOH. After stirringunder Ar for 3 h, the mixture was neutralized with 1 M H₂PO₄ to pH 7.2under Ar. The mixture was added dropwise to the solution of 10.0 g (32.2mmol) of 1,2-bis(5-nitropyridin-2-yl)disulfane in 200 ml of DMA. Afterstirring for 4 h under Ar, the mixture was concentrated, diluted withwater, filtered, evaporated and purified with C-18 4.0×20 cm columneluted with water/methanol (95:5) to afford 3.1 g (75% yield) of thetitle compound. m.p.=288˜291° C. (decomp.) 1H NMR (DMF-d7) 9.29 (d, 1H,J=2.2 Hz), 8.63 (dd, 1H, J=2.7, 8.9 Hz), 8.17 (d, 1H, J=8.9 Hz), 3.73(t, 1H, J=7.2 Hz), 3.22˜3.17 (m, 1H), 3.15˜3.10 (m, 1H), 2.41˜2.33 (m,2H); 13C NMR 170.92, 169.10, 146.04, 143.67, 133.65, 120.72, 64.22,37.82, 29.26; MS m/z− 352.8 (M−H).

1-(2,5-dioxopyrrolidin-1-yloxy)-4-((5-nitropyridin-2-yl)disulfanyl)-1-oxobutane-2-sulfonicAcid

220 mg (0.62 mmol) of4-((5-nitropyridin-2-yl)disulfanyl)-2-sulfobutanoic acid in 15 DMA wasadded 130 mg (1.13 mmol) of NHS and 480 mg (2.50 mmol) of EDC. Themixture was stirred under Ar overnight, evaporated and purified on SiO₂chromatography eluted with CH₂CH₂/CH₃OH/HCOOH (10000:1000:1 to10000:1500:1) to afford 227 mg (82% yield) of the title compound. 1H NMR(DMSO-d6) 9.25 (d, 1H, J=5.2 Hz), 8.57 (dd, 1H, J=2.5, 8.9 Hz), 8.04 (t,1H, J=8.0+8.9 Hz), 3.86 (dd, 1H, J=4.9, 9.7 Hz), 3.13˜3.12 (m, 2H), 2.76(s, 4H), 2.36˜2.30 (m, 1H), 2.25˜2.21 (m, 1H); 13C NMR 166.96, 165.01,144.93, 142.26, 132.63, 119.61, 61.00, 35.03, 29.30, 25.39; MS m/z−449.8 (M−H).

4-(pyridin-2-yldisulfanyl)-2-sulfobutanoic Acid

1.5 g (5.85 mmol) of 4-(Acetylthio)-1-methoxy-1-oxobutane-2-sulfonicacid was added to 100 ml of 0.5 M NaOH solution. After stirring under Arfor 3 h, the mixture was concentrated to ˜50 ml and neutralized with 1 MH₂PO₄ to pH 7.2 under Ar. The mixture was added dropwise to the solutionof 4.0 g (18.1 mmol) of 2,2′-dithiodipyridine in 60 ml of DMA. Afterstirring for 4 h under Ar, the mixture was concentrated, diluted withwater, filtered, evaporated and purified with C-18 4.0×20 cm columneluted with water/methanol (99:1 to 90:10) to afford 1.32 g (73% yield)of the title compound. 1H NMR (DMF-d7) 8.39 (dd, 1H, J=3.5, 4.8 Hz),7.86 (m, 2H), 7.25 (m, 1H), 3.59 (dd, 1H, J=5.2, 9.4 Hz), 2.90 (m, 2H),2.28 (m, 2H); 13C NMR 172.60, 159.16, 148.93, 138.09, 121.03, 119.38,67.49, 36.39, 28.666; MS m/z− 307.8 (M−H).

1-(2,5-dioxopyrrolidin-1-yloxy)-1-oxo-4-(pyridin-2-yldisulfanyl)butane-2-sulfonicAcid

680 mg (2.20 mmol) of 4-(pyridin-2-yldisulfanyl)-2-sulfobutanoic acid in50 DMA was added 300 mg (2.60 mmol) of NHS and 800 mg (4.16 mmol) ofEDC. The mixture was stirred under Ar overnight, evaporated and purifiedon SiO₂ chromatography eluted with CH₂CH₂/CH₃OH/HCOOH (10000:1000:1 to10000:1500:1) to afford 720 mg (80% yield) of the title compound. 1H NMR(DMSO-d6) 8.40 (dd, 1H, J=3.5, 4.7 Hz), 7.85 (m, 2H), 7.24 (m, 1H), 3.58(dd, 1H, J=5.1, 9.4 Hz), 2.94˜2.90 (m, 2H), 2.74 (s, 4H), 2.31˜2.27 (m,2H); 13C NMR 168.16, 161.11, 147.91, 139.22, 121.63, 119.31, 66.80,36.30, 28.36, 25.42; MS m/z−404.9 (M−H).

3,6-endoxo-Δ-tetrahydrophthalhide

Maleimide (5.0 g, 51.5 mmol) in ethylether (200 ml) was added furan (5.5ml, 75.6 mmol). The mixture was heated inside a 1 L of autoclave bomb at100° C. for 8 h. The bomb was cooled down to room temperature, and theinside solid was rinsed with methanol, concentrated and crystallized inethyl acetate/hexane to afford 8.4 g (99%) of the title compound. 1H NMR(DMF-d7): 11.08 (s, 1H) (NH), 6.60 (m, 2H), 5.16 (m, 2H), 2.95 (m, 2H).13C NMR 178.84, 137.69, 82.00, 49.92. MS m/z+188.4 (MW+Na).

Methyl 4-N-(3, 6-endoxo-Δ-tetrahydrophthalido)-2-sulfo-butyrate

3, 6-Endoxo-Δ-tetrahydrophthalhide (0.80 g, 4.85 mmol) in DMA (20 ml)was added K2CO3 (1.4 g, 10.13 mmol) and KI (0.19 g, 1.14 mmol). Afterstirring under Ar for 1 hr, methyl 4-bromo-2-sulfo-butyrate (0.98 g,3.77 mmol) in DMA (10 ml) was added. The mixture was stirred under Arovernight, evaporated, re-dissolved in 1% HAc in methanol, filtered,evaporated and purified by SiO2 chromatography and eluted with 1:5:0.01to 1:4:0.01 CH3OH/CH2C12/HAc to afford 0.98 (75%) g of the titlecompound. 1H NMR (DMF-d7): 6.59 (m, 2H), 5.16 (dd, 2H, J=0.8, 7.8 Hz),3.65-3.63 (m, 3H), 3.47 (m, 2H), 3.01 (s, 3H), 2.83 (m, 2H). 13C NMR172.94, 162.86, 137.68, 81.98, 52.39, 49.91, 48.58, 36.01, 21.97. MSm/z−343.9 (MW-H).

Methyl 4-N-maleimido-2-sulfo-butyrate

In an opened round bottom flask, methyl 4-N-(3,6-endoxo-Δ-tetrahydrophthalido)-2-sulfo-butyrate (0.30 g, 0.87 mmol) in20 ml of 1:1 DMA/100 mM NaH₂PO₄, pH 7.0 was heated at 120˜140° C. for 4h. During the reaction time, 5×10 ml of water was gradually added tokeep the reaction volume around 15 ml. The mixture was concentrated todryness and purified by SiO₂ chromatography eluted with 1:5:0.01 to1:4:0.01 CH₃OH/CH₂Cl₂/HAc to afford 0.230 g (95%) of the title compound.¹H NMR (DMF-d7): 6.60 (s, 2H), 4.06 (d, 1H), 3.60 (m, 3H), 3.47 (m, 2H),2.43 (m, 2H); ¹³C NMR 171.59, 164.96, 136.10, 66.20, 51.71, 34.82,22.10. MS m/z− 276.6 (MW-H).

Methyl 4-azido-2-sulfo-butyrate

Methyl 4-bromo-2-sulfo-butyrate (1.07 g, 4.11 mmol) and sodium azide(0.70 g (10.7 mmol) in DMF (50 ml) was stirred overnight. The mixturewas evaporated and purified by SiO₂ chromatography and eluted with1:5:0.01 CH₃OH/CH₂Cl₂/HAc and crystallized with CH₃OH/Toluene/Hexane toafford 1.00 g (95%) of the title compound. m.p=267-272° C. (decomp). 1HNMR (DMF-d7): 12.06 (br, 1H), 3.65 (s, 3H), 3.59 (dd, 1H, J=5.4, 8.9Hz), 3.47 (m, 2H), 2.24 (m, 2H). ¹³C NMR 171.10, 64.29, 52.24, 50.64,21.35. ESI MS m/z+267.9 (M+2Na—H), m/z− 222.0 (M−H). HRMS m/z−(C₅H₉N₃O₅S—H) calcd 222.0185, found 222.0179.

4-azido-2-sulfo-butyric Acid

Methyl 4-azido-2-sulfo-butyrate (1.00 g, 4.08 mmol) in the mixture ofHCl (50 ml, 1.0 M) and HAC (5 ml) was heated at 100° C. for 8 hrs. Themixture was evaporated and co-evaporated 3×50 ml of water, andcrystallized with water/acetone to afford 1.0 g (99%) of the titlecompound. ¹H NMR (DMF-d₇): 3.60 (m, 2H), 3.52 (m, 1H), 2.24 (m, 2H). ¹³CNMR 170.96, 63.04, 50.66, 29.12. ESI MS m/z− 207.7 (MW-H); HRMS m/z−(C₄H₇N₃O₅S—H) calcd 208.0028, found 208.0021.

4-Amino-2-sulfo-butyric Acid

4-Azido-2-sulfo-butyric acid (500 mg, 2.40 mmol), water (20 ml) and Pd/C(110 mg, 10% Pd, 50% water based) were placed into a 250 mlhydrogenation shaking bottle. After the air in the bottle was sucked outby a vacuum, 20 psi of hydrogen was let into the bottle. The mixture wasshaken for 8 h, then filtered through celite, washed with DMF,evaporated and co-evaporated with dry DMF to afford 476 mg (91% HClsalt) of the title product. ESI MS m/z− 181.8 (MW-H). This product wasused directly without further purification.

(Z)-4-(3-carboxy-3-sulfopropylamino)-4-oxobut-2-enoic Acid

The above 4-Amino-2-sulfo-butyric acid, HCl salt (476 mg, 2.16 mmol) indry DMF (20 ml) was added maleic anhydride (232 mg, 2.36 mmol). Themixture was stirred under Ar overnight, evaporated and purified on selfpacked c-18, ϕ1.0×25 cm column, eluted with water. The fractionscontained product were pooled, evaporated and crystallized withH₂O/acetone to afford 552 mg (91%) of the title product. ¹H NMR(DMF-d7): 9.70 (br, 1H), 6.73 (d, 1H, J=12.8 Hz), 6.32 (d, 1H, J=12.8Hz), 3.69 (m, 1H), 3.47 (m, 2H), 2.27 (m, 2H). ¹³C NMR 171.47, 167.32,165.87, 135.44, 133.07, 63.82, 39.13, 27.62. ESI MS m/z− 279.8 (MW-H);HRMS m/z− (C₈H₁₁NO₈S—H) calcd 280.0127, found 280.0121.

4-N-Maleimido-2-sulfo-butanoic Acid

(Z)-4-(3-carboxy-3-sulfopropylamino)-4-oxobut-2-enoic acid (310 mg, 1.10mmol) in mixture dry DMA (5 ml) and dry toluene (20 ml) was heated.After the temperature reached at 80° C., HMDS (hexamethyldisilazane)(1.40 ml, 6.71 mmol) and ZnCl₂ (1.85 ml, 1.0 M in diethyl ether, 1.85mmol) was added. The mixture was continued heated to 115˜125° C. andtoluene was collected through Dean-Stark trap. The reaction mixture wasfluxed at 120° C. for 6 h. During this period, 2×20 ml of dry toluenewas added to keep the mixture volume around 8˜10 ml. Then the mixturewas cooled, 1 ml of 1:10 HCl (conc)/CH₃OH was added, evaporated,purified on SiO₂ chromatography eluted with CH₃OH/CH₂Cl₂/HAc (1:5:0.01to 1:4:0.01) to afford 260 mg (92%) of the title product. ¹H NMR(DMF-d₇): 10.83 (br, 1H), 6.95 (s, 2H), 1H, J=12.8 Hz), 3.65 (m, 1H),3.54 (m, 2H), 2.27 (m, 2H). ¹³C NMR 173.61, 172.04, 135.47, 64.18, 37.1,27.89. ESI MS m/z− 261.8 (MW-H). HRMS m/z− (C₈H₉NO₇S—H) calcd 262.0021,found 262.0027.

Succinimidyl 4-N-maleimido-2-sulfo-butyrate

4-N-maleimido-2-sulfo-butanoic acid (260 mg, 0.99 mmol) in DMA (10 ml)was added to NHS (220 mg, 1.91 mmol) and EDC (500 mg, 2.60 mmol). Themixture was stirred under Ar overnight, evaporated and purified on SiO₂chromatography eluted with CH₂CH₂/CH₃OH/HAc (10000:1000:1 to10000:2000:1), then crystallized with DMA/EtAc/Hexane to afford 285 mg(81% yield) of the title compound. ¹H NMR (DMF-d7) 6.99 (s, 1H), 3.83(m, 1H), 3.64 (m, 2H), 2.75 (s, 4H), 2.34 (m, 2H); ¹³C NMR 171.97,171.82, 166.64, 135.58, 62.00, 36.66, 26.62; ESI MS m/z− 358.9 (M−H);HRMS m/z− (C₁₂H₁₂N₂O₉S—H) calcd 359.0185, found 359.0178.

(E)-Methyl 4-azidobut-2-enoate

To the solution of NaN₃ (2.80 g, 43.01 mmol) in 100 ml of DMF at −20° C.was added methyl 4-bromocrotonate (5.00 ml, 85%, 36.10 mmol). Afterstirred at −20° C. for 30 min, the mixture was stirred at 0° C. for 4 h,evaporated, suspended with EtAc/Hexane (1:1), filtered, evaporated andchromatographic purification on SiO₂ column eluted with EtAc/Hexane(1:25 to 1:10) to afford HRMS for 4.08 g (80%) of the title product. ¹HNMR (CDCl₃) 6.88 (m, 1H), 6.06 (ddd, 1H, J−=1.7, 3.4, 15.6 Hz), 3.97(dd, 2H, J=1.2, 4.96 Hz), 3.73 (s, 3H); ¹³C NMR 166.23, 140.86, 123.49,51.95, 51.36; ESI MS m/z+182.5 (M+Na+H₂O); HRMS m/z+ (C₅H₇N₃O₂+H₂O+Na)calcd 182.0542, found 182.0548.

Methyl 3-(acetylthio)-4-azidobutanoate

To the solution of (E)-Methyl 4-azidobut-2-enoate (4.00 g, 28.37 mmol)in 60 ml of THF at 0° C. was added the mixture of thiolacetic acid (3.0ml, 42.09 mmol) and DIPEA (8.0 ml, 45.92 mmol) in 60 ml of THF in 20min. After stirred at 0° C. for 1 hr, the mixture was stirred at RTovernight, evaporated, redissolved in CH₂Cl₂, washed with NaHCO₃ (sat.)and 1 M NaH₂PO₄/NaCl (sat.), pH 4 respectively, dried over MgSO4,filtered, evaporated and chromatographic purification on SiO₂ columneluted with EtAc/Hexane (1:8 to 1:4) to afford HRMS for 4.98 g (81%) ofthe title product. ¹H NMR (CDCl₃) 3.66 (m, 1H), 3.62 (s, 3H), 3.40 (dd,1H, J=7.5, 12.7 Hz), 3.31 (m, 1H), 2.78 (m, 1H), 2.60 (m, 1H), 2.32 (s,3H); ¹³C NMR (DMF-d7) 192.20, 172.48, 56.56, 53.60, 51.31, 34.58, 30.56;ESI MS m/z+240.0 (M+Na), 255.9 (M+K); HRMS m/z+ (C₇H₁₁N₃O₃S+Na) calcd240.0419, found 240.0415.

Azido-4-methoxy-4-oxobutane-2-sulfonic Acid

Methyl 3-(acetylthio)-4-azidobutanoate (4.00 g, 18.43 mmol) in 75 ml ofacetic acid was added 25 ml of H₂O₂ (30%). The mixture was stirredovernight, evaporated and co-evaporated with EtOH/toluene and purifiedon SiO₂ chromatography eluted with CH₃OH/CH₂Cl₂/HAc (100:800:1 to100:500:1) to afford 3.85 (93%) g the title compound. ¹H NMR (CD₃OD)3.78 (dd, 1H, J=5.0, 12.7 Hz), 3.62 (s, 3H), 3.44 (dd, 1H, J=7.5, 12.7Hz), 3.33 (m, 1H), 2.84 (dd, 1H, J=5.6, 16.5 Hz), 2.57 (dd, 1H, J=7.5,16.5 Hz); ¹³C NMR (DMF-d7) 173.37, 57.31, 52.54, 52.49, 34.51; ESI MSm/z− 221.7 (M+H).

4-Azido-3-sulfobutanoic Acid

Azido-4-methoxy-4-oxobutane-2-sulfonic acid (3.80 g, 17.04 mmol) in 150ml of 1.0 M HCl was added 8.0 ml of HAc. The mixture was refluxed at120° C. overnight, evaporated and co-evaporated with water, EtOH,EtOH/toluene respectively and purified on SiO₂ chromatography elutedwith CH₃OH/CH₂Cl₂/HAc (100:500:1 to 100:400:1) to afford 3.02 (85%) gthe title compound. ¹H NMR (CD₃OD) 3.77 (dd, 1H, J=5.1, 12.8 Hz), 3.45(dd, 1H, J=7.0, 12.8 Hz), 3.31 (m, 1H), 2.86 (dd, 1H, J=4.7, 16.7 Hz),2.51 (dd, 1H, J=8.4, 16.7 Hz); ¹³C NMR (DMF-d7) 173.98, 67.50, 59.78,27.82; ESI MS m/z− 207.7 (M−H).

4-amino-3-sulfobutanoic Acid

In a 500 ml of hydrogenation bottle was added 4-azido-3-sulfobutanoicacid (3.00 g, 14.35 mmol), 150 ml of methanol and 0.32 g of Pd/C (10%Pd, 50% wet). After sucked out air, 30 psi of H2 was conducted, and themixture was shaken overnight, filtered through celite, evaporated, andcoevaporated with dry EtOH to afford about 2.50 g (95%) of4-amino-3-sulfobutanoic acid. ¹H NMR (CD₃OD) 3.24 (m, 1H), 3.17 (m, 1H),2.90 (dd, 1H, J=2.6, 16.5 Hz), 2.33 (dd, 1H, J=10.1, 16.5 Hz), ESI MSm/z− 181.60 (M−H). The resulted compound was unstable and was useddirectly without further purification.

(Z)-4-(3-carboxy-2-sulfopropylamino)-4-oxobut-2-enoic Acid

To the solution of 4-amino-3-sulfobutanoic acid (˜2.50 g, 13.66 mmol) in100 ml of DMA was added maleic anhydride (1.48 g, 15.10 mmol) and themixture was stirred over night, evaporated, purified on C-18 column(2×30 cm) eluted with 1% HAc in water and crystallized withMeOH/Acetone/toluene to afford 3.34 g (83%) of(Z)-4-(3-carboxy-2-sulfopropylamino)-4-oxobut-2-enoic acid. ¹H NMR(CD₃OD) 6.33 (d, 1H, J=12.6 Hz), 6.10 (d, 1H, J=12.6 Hz), 3.64 (dd, 1H,J=5.8, 14.0 Hz), 3.54 (m, 1H), 3.30 (m, 1H), 2.78 (dd, 1H, J=4.9, 16.8Hz), 2.39 (m, 1H); ¹³C NMR 173.52, 168.68, 167.98, 135.59, 127.79,57.31, 40.56, 34.52; ESI MS m/z− 279.7 (M−H).

4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)-3-sulfobutanoic Acid

(Z)-4-(3-carboxy-2-sulfopropylamino)-4-oxobut-2-enoic acid (450 mg, 1.60mmol) in mixture of 10 ml of dry DMA and 50 ml of dry toluene washeated. After the temperature reached at 80° C., HMDS(hexamethyldisilazane, 1.80 ml, 8.63 mmol,) and ZnCl₂ (3.2 ml, 1.0 M indiethyl ether) were added. The mixture was continued heated to 115˜125°C. and toluene was collected through Dean-Stark trap. The reactionmixture was fluxed at 120° C. for 6 h. During this period, 2×20 ml ofdry toluene was added to keep the mixture volume around 8˜10 ml. Thenthe mixture was cooled, 1 ml of 1:10 HCl (conc)/CH₃OH was added,evaporated, purified on SiO₂ chromatography eluted with 1:5:0.01CH₃OH/CH₂Cl₂/HAc to afford 315 mg (75%) of the title product. ¹H NMR(DMF-d7) 6.96 (s, 2H), 4.04 (dd, 1H, J=4.3, 13.8 Hz), 3.47 (m, 1H), 3.23(dd, 1H, J=7.4, 14.7 Hz), 2.99 (dd, 1H, J=3.3, 16.8 Hz), 2.35 (dd, 1H,J=8.1, 16.9 Hz); ¹³C NMR 173.58, 172.18, 135.54, 54.61, 40.24, 32.43,ESI MS m/z− 261.70 (M−H).

1-(2,5-Dioxo-2,5-dihydro-1H-pyrrol-1-yl)-4-(2,5-dioxopyrrolidin-1-yloxy)-4-oxobutane-2-sulfonicAcid

4-(2,5-Dioxo-2,5-dihydro-1H-pyrrol-1-yl)-3-sulfobutanoic acid (110 mg,0.418 mmol), EDC (240 mg, 1.25 mmol) and N-hydroxysuccinimide (58 mg,0.504 mmol) was stirred in 10 ml of DMA for overnight, evaporated andpurified on SiO₂ chromatography eluted with CH₃OH/CH₂Cl₂/HAc (100:900:1to 100:600:1) to afford 112 mg (75%) of the title product. ¹H NMR(DMF-d7) 6.93 (s, 2H), 4.06 (dd, 1H, J=4.8, 13.1 Hz), 3.80 (dd, 1H,J=10.7, 13.9 Hz), 3.35 (dd, 1H J=3.3, 17.8 Hz), 3.25 (m, 1H), 3.10 (dd,1H, J=2.2, 16.4 Hz), 2.87 (m, 4H); ¹³C NMR 172.27, 170.88, 169.29,135.55, 55.28, 40.22, 32.69, 26.66; ESI MS m/z− 261.70 (M−H).

Ethyl 3-(acetylthio)-3-cyanopropanoate

(Z)-ethyl 3-cyanoacrylate (5.01 g, 40.00 mmol) in 80 ml of THF at −20°C. was added the solution of thiol acetic acid (5.0 ml, 70.15 mmol) andDIPEA (16.0 ml, 92.03 mmol) in 20 ml of THF in 30 min. The reaction waskept at −20° C. for 4 hr then room temperature overnight. The mixturewas concentrated, diluted with CH₂Cl₂, washed with saturated NaHCO₃,dried over MgSO₄, filtered, evaporated and purified by SiO₂chromatography (1:4 EtAC/Hexane) to afford 5.22 g (65%) of the titlecompound. Rf=0.25 (1:4 EtAC/Hexane); ¹H NMR (CDCl₃), 4.44 (m, 1H), 4.11(dd, 2H, J=7.1, 14.3 Hz), 3.38 (m, 1H), 3.15 (m, 1H), 2.17 (s, 3H), 1.19(t, 3H, J=7.2 Hz); ¹³C NMR 194.12, 173.21, 119.82, 61.35, 33.52, 30.08,14.62; MS m/z+225.9 (MW+Na), m/z− 201.7 (MW-H).

Cyano-3-ethoxy-3-oxopropane-1-sulfonic Acid

Ethyl 3-(acetylthio)-3-cyanopropanoate (2.00 g, 9.95 mmol) in aceticacid (40 ml) was added H₂O₂ (12 ml, 30%). The mixture was stirredovernight, evaporated and purified on silica gel chromatography elutedwith methanol/dichloromethane/acetic acid (1:8:0.01 to 1:5:0.01) toafford 1.72 g (84%) of the title compound. ¹H NMR (DMSO), 4.63 (m, 1H),4.12 (dd, 2H, J=7.1, 14.3 Hz), 3.27 (m, 1H), 3.05 (m, 1H), 1.28 (t, 3H,J=7.2 Hz); ¹³C NMR 173.15, 113.85, 61.38, 48.32, 26.33, 14.15; MS m/z−205.7 (MW-H).

1-(tert-Butoxycarbonylamino)-4-ethoxy-4-oxobutane-2-sulfonic Acid

In a hydrogenation bottle was addedCyano-3-ethoxy-3-oxopropane-1-sulfonic acid (2.50 g, 12.06 mmol),ethanol (80 ml), fresh filtered Raney Nickel (0.40 g) and BOC anhydride(3.30 g, 15.12 mmol). After the air inside the bottle was sucked out byvacuum, 20 psi of hydrogen was conducted to the bottle. The bottle wasshaken over night, filtered through celite, evaporated, and purified onsilica gel chromatography eluted with methanol/dichloromethane/aceticacid (1:6:0.01) to afford 3.18 g (85%) of the title compound. ¹H NMR(DMSO), 6.82 (s, 1H), 4.26 (m, 1H), 4.11 (dd, 2H, J=7.1, 14.3 Hz), 3.53(dd, 1H, J=4.2, 13.4 Hz), 3.36 (m, 1H), 2.86 (m, 1H), 2.51 (m, 1H), 1.38(s, 9H), 1.22 (t, 3H, J=7.2 Hz); ¹³C NMR 173.35, 155.72, 80.44, 62.05,52.55, 41.61, 34.50, 28.85, 14.52; MS m/z− 309.8 (MW-H).

4-(tert-butoxycarbonylamino)-3-sulfobutanoic Acid

1-(tert-Butoxycarbonylamino)-4-ethoxy-4-oxobutane-2-sulfonic acid (402mg, 1.29 mmol) in the mixture of THF/H₂O (1:2, 60 ml) was added lithiumhydroxide monohydrate (2.0 g, 47.6 mmol). The mixture was stirred underAr overnight, concentrated, purified on C-18 column (2×30 cm) elutedwith from 100% water to 10% methanol in water to afford 328 mg (90%) ofthe title compound. ¹H NMR (DMSO), 6.78 (s, 1H), 4.03 (m, 1H), 3.57 (dd,1H, J=4.2, 13.4 Hz), 3.41 (m, 1H), 2.89 (m, 1H), 2.61 (m, 1H), 1.39 (s,9H); ¹³C NMR 174.21, 155.82, 79.85, 59.95, 42.06, 32.52, 28.88, 14.55;ESI MS 281.8 (M−H).

(Z)-4-(3-carboxy-2-sulfopropylamino)-4-oxobut-2-enoic Acid

4-(Tert-butoxycarbonylamino)-3-sulfobutanoic acid (321 mg, 1.13 mmol)was stirred in the mixture of HCl (conc)/Dioxane (1:4, 15 ml) for 30min, evaporated and coevaporated with EtOH/Toluene (1:1, 4×20 ml) todryness. To the dryness material was added maleic anhydride (121 mg,1.23 mmol) and DMA (20 ml) and the mixture was stirred overnight,evaporated and run through C-18 column eluted with water andcrystallized with EtOH/Hexane to afford 263 mg (83%) of the titlecompound. ESI MS 279.8 (M−H). The NMR data are the same through theroute with 4-azido-3-sulfobutanoic acid.

N,N,N-trimethyl-2-oxotetrahydrothiophen-3-aminium

3-aminodihydrothiophen-2(3H)-one hydrochloride (6.00 g, 39.1 mmol),sodium bicarbonate (3.28 g, 39.1 mmol) and iodomethane (13 mL, 209 mmol)were stirred in dry methanol (100 ml) overnight, filtered throughcelite, evaporated, purified on SiO2 column eluted with MeOH/CH₂Cl₂/HAc(1:5:0.01), and crystallized with EtOH/Hexane to afford 5.25 g (84%) ofthe title product. mp 228-231° C. ¹H NMR (CD₃OD) 4.27 (m, 1H), 3.25 (s,9H), 2.56-2.47 (m, 2H), 2.34 (m, 1H), 2.26 (m, 1H); ¹³C NMR 168.97,75.06, 53.25, 30.85, 16.46; ESI MS m/z+160.0 (M+).

1-carboxy-N,N,N-trimethyl-3-(pyridin-2-yldisulfanyl)propan-1-aminium

N,N,N-trimethyl-2-oxotetrahydrothiophen-3-aminium acetate (2 g, 9.13mmol) was stirred in 75 ml of 1 M NaOH (3 g NaOH in 75 ml H₂O) for 45min. neutralized with 4 M H₃PO₄ to pH 7.4, concentrated, added to1,2-di(pyridin-2-yl)disulfane (11 g, 49.9 mmol) in 200 ml of MeOH. Themixture was stirred over night, extracted with EtAc. The aqueoussolution was evaporated, suspended with MeOH, filtered salt, evaporatedand purified on C-18 column (2 cm×30 cm) eluted with water/methanol (100water to 20% methanol/water) to afford 2.6 g (75%) of the title product.ESI MS m/z+309.1 (M+Na-H).

1. Modification of Antibody with Sulfo Linker

The huC242 is modified with sulfo linker at 8 mg/mL antibody, a 15 foldmolar excess of sulfo linker (˜30 mM stock solution in DMA). Thereaction is carried out in 100 mM NaPi, pH8.0 buffer with DMA (5% v/v)for 15, 30, 120, and 200 minutes at 25° C. The modified huC242 waspurified by G25 column with 50 mM NaPi, 50 mM NaCl, and 2 mM EDTA, pH6.5to remove the excess sulfo linker.

2. Measurement of Releasable Spy-NO₂ and Antibody Concentration ofModified huC242

The assay and spectral measurement were carried in 100 mM NaPi, pH7.5 atroom temperature. The molar ratio of Spy-NO₂ released per mole of huC242antibody was calculated by measuring the A₂₈₀ of the sample and then theincrease in the A₃₉₄ of the sample after adding DTT (50 μL of 1 M DTT/mLof sample). The concentration of DTT-released 2-mercaptopyridine iscalculated using a ε_(394 nm) of 14,205 M⁻¹cm⁻¹. The concentration ofantibody can then be calculated using ε_(280 nm) of 217,560 M⁻¹ cm⁻¹after subtracting the contribution of Spy-NO₂ absorbance at 280 nm(A_(394 nm) post DTT×3344/14205) from the total A_(280 nm) measuredbefore DTT addition. The molar ratio of Spy-NO₂:Ab can then becalculated. The mg/mL (g/L) concentration of huC242 is calculated usinga molecular weight of 147,000 g/mole.

3. Conjugation Reaction

The modified huC242 was reacted with a 1.7-fold molar excess of DM4(based on DM4 stock SH concentration) over Spy-NO₂. The reaction iscarried out at 2.5 mg/mL antibody in 50 mM NaPi, 50 mM NaCl, 2 mM EDTA,pH6.5 and DMA (5% v/v). After addition of DM4, the reaction wasincubated 25° C. for ˜20 hours. The final conjugate was purified by G25column with 10 mM Histidine, 130 mM Glycine, 5% sucrose, pH5.5 to removethe excess DM4 drug.

4. Calculation of huC242 and DM4 Concentration

The huC242 and DM4 both absorb at the two wavelengths used to measureeach component separately, i.e., 280 and 252 nm. The extinctioncoefficient at 280 nm for huC242 is 217,560 and for DM4 is 5180 M⁻¹. The252 nm/280 nm absorbance ratios of huC242 and DM4 are 0.368 and 5.05respectively. The concentrations were calculated with following equation

$C_{D} = {{\frac{A_{252} - {0.368A_{280}}}{24692.4}C_{Ab}} = \frac{A_{280} - {5180C_{D}}}{217,560}}$Results

Modification time L/A D/A Monomer ratio Free drug %  15 min 5.0 4.196.7% N/D*  30 min 6.1 5.4 96.2% <1% 120 min 6.6 6.8 95.7% <1% 200 min6.6 6.3 95.9% <1%C242-Sulfo-DM4 Linker Titration

% Linker DM4 mg/mL μg/mL % Free Excess L:A xs D:A Ab DM4 Monomer Drug 52.4 1.7 1.9 0.83 8.2 95 0 10 4.1 1.7 3.3 0.83 14.4 94 0 15 5.6 1.7 4.60.82 20.0 93 0 20 7.3 1.7 6.0 0.82 25.8 91 0 25 9.1 1.3 6.6 0.79 27.7 920.6 30 10.4 1.3 7.6 0.68 27.5 94 1.1 35 12.2 1.3 8.2 0.67 26.7 95 1.6Conjugation Protocol:

Modification was done at pH 8.0, buffer A and 5% DMA for 90 min at roomtemperature, the antibody concentration is 7 mg/ml. The modificedantibody was purified by NAP column using Buffer A pH6.5. Theconjugation was down at Buffer A, pH6.5 with 5-10% DMA at roomtemperature overnight. The drug to linker ratio ranged from 1.3 to 1.7deepening on the total drug added.

Example 2: Conjugate Synthesis

SPP or SSNPP linker was dissolved in ethanol at a concentration ofapproximately 10 mM. Antibody was dialyzed into buffer A (50 mM KPi, 50mM NaCl, 2 mM EDTA, pH 6.5). For the linker reaction, the antibody wasat 8 mg/ml, and 7 equivalents of linker were added while stirring in thepresence of 5% (v/v) ethanol. The reaction was allowed to proceed atambient temperature for 90 minutes. Unreacted linker was removed fromthe antibody by Sephadex G25 gel filtration using a Sephadex G25 columnequilibrated with Buffer A at pH 6.5 or 150 mM potassium phosphatebuffer containing 100 mM NaCl, pH 7.4 as indicated. For the SPP linker,the extent of modification was assessed by release of pyridine-2-thioneusing 50 mM DTT and measuring the absorbance at 343 nm as describedbelow (ε343=8080 M⁻¹ cm⁻¹ for free pyridine-2-thione). For SSNPP,modification was assessed directly by measuring the absorbance at 325 nm(£₃₂₅=10,964 M⁻¹ cm⁻¹ for the 4-nitropyridyl-2-dithio group linked toantibody). For the conjugation reaction, thiol-containing drug (eitherDM1 or DC4) was dissolved in DMA (N, N-dimethylacetamide) at aconcentration of approximately 10 mM. The drug (0.8-1.7-fold molarexcess relative to the number of linker molecules per antibody asindicated) was slowly added with stirring to the antibody which was at aconcentration of 2.5 mg/ml in buffer A (pH 6.5 or pH 7.4) in a finalconcentration of 3% (v/v) DMA. The reaction was allowed to proceed atambient temperature for the indicated times. Drug-conjugated antibodywas purified using a Sephadex G25 column equilibrated with buffer B(PBS, pH 6.5). For DML, the extent of drug conjugation to antibody wasassessed by measuring A₂₅₂ and A₂₈₀ of the conjugate as described below.A similar approach was used for DC4 (see below).

Measurement of Releasable Pyridine-2-thione and Ab Concentration ofSPP-Modified Ab.

The molar ratio of pyridine-2-thione released per mole of antibody iscalculated by measuring the A₂₈₀ of the sample and then the increase inthe A₃₄₃ of the sample after adding DTT (50 μL of 1 M DTT/mL of sample).The concentration of DTT-released pyridine-2-thione is calculated usingan ε₃₄₃ of 8080 M⁻¹cm⁻¹. The concentration of antibody can then becalculated using an ε₂₈₀ of 194,712 M⁻¹cm⁻¹ after subtracting thecontribution of pyridine-2-thione absorbance at 280 nm (A_(343 nm) postDTT×5100/8080) from the total A_(280 nm) measured before DTT addition.The molar ratio of pyridine-2-thione:Ab can then be calculated. Themg/mL (g/L) concentration of Ab is calculated using a molecular weightof 147,000 g/mole.

Measurement of antibody-linked 5-Nitropyridyl-2-dithio Groups and AbConcentration of SSNPP-Modified Ab.

The molar ratio of the 4-nitropyridyl-2-dithio groups linked per mole ofantibody is calculated by measuring the A₂₈₀ and A₃₂₅ of the samplewithout DTT treatment. The number of antibody-bound4-nitropyridyl-2-dithio groups is calculated using an ε_(325 nm) of10,964 M⁻¹cm⁻¹. The concentration of antibody can then be calculatedusing an ε₂₈₀ nm of 194,712 M⁻¹cm¹ after subtracting the contribution ofthe 5-nitropyridyl-2-dithio group absorbance at 280 nm(A_(325 nm)×3344/10964) from the total A_(280 nm) measured. The molarratio of 4-nitropyridyl-2-dithio groups:Ab can then be calculated. Themg/mL (g/L) concentration of Ab is calculated using a molecular weightof 147,000 g/mole.

Calculating Ab and DM1 component concentrations of Ab-DM1.

The Ab and DM1 both absorb at the two wavelengths used to measure eachcomponent separately, i.e., 280 and 252 nm. The components arequantified using the following algebraic expressions which account forthe contribution of each component at each wavelength (C_(Ab) is themolar concentration of Ab and C_(D) is the molar concentration of DM1):

1) Total A₂₈₀=194,712C_(Ab)+5,700C_(D)

2) Total A₂₅₂=(194,712×0.37)C_(Ab)+(4.7×5,700) C_(D)

Each equation is solved for C_(Ab):

$\begin{matrix}{C_{Ab} = \frac{A_{180} - {5,700C_{D}}}{194,712}} & \left. {1a} \right) \\\frac{C_{Ab} = {A_{252} - {26,790C_{D}}}}{72,043} & \left. {2a} \right)\end{matrix}$

and an equality is set up (equation 1a=equation 2a) and solved forC_(D):

$C_{D} = \frac{A_{252} - {0.37A_{280}}}{24,681}$

Once the C_(D) is calculated, the value is used to solve for C_(Ab) inequation 1a (or 2a) above. The ratio of DM1:Ab can then be calculated.The mg/mL (g/L) concentration of antibody is calculated using amolecular weight of 147,000 g/mole and the concentration of DM1 iscalculated using a molecular weight of 736.5 g/mole (linked DM1)

Efficiency of Disulfide Exchange is Increased with SSNPP.

As shown in Table 1, the efficiency of conjugation is enhanced inreactions where SSNPP is used as the cross-linker compared to reactionsusing SPP. The percent efficiency was calculated by dividing the valuefor DM1 per antibody by the linker per antibody ratio times 100.Conjugations of the N901 antibody using SSNPP resulted in cross-linkingefficiencies of 93% at both pH 6.5 and 7.4. The efficiency ofconjugation of N901 with SPP in these experiments was 70% at pH 6.5 and77% at pH 7.4. The increased efficiency with SSNPP demonstrates that atarget DM1 to antibody ratio can be achieved using antibody that ismodified with a reduced number of linker molecules. In fact, a similardrug to antibody ratio (4.3) was achieved in the final conjugate with anantibody preparation having 4.2 (5-nitropyridyl-2-dithio)-groups perantibody introduced with SSNPP compared to an antibody having 5.6pyridyl-2-dithio groups introduced with SPP (Table 2). The amount ofdrug required to obtain comparable conjugation results was therefore 25%lower for the SSNPP-modified antibody than the SPP-modified antibodyunder these conditions. An additional potential benefit of the increasedefficiency with SSNPP is that a reduced molar excess of DM1 may be usedin the conjugation reaction. A comparison of the DM1 per antibody ratiosfollowing conjugation with a range of drug equivalents in the reaction(0.8-1.7 fold excess) shows that a 1.1-fold molar excess is sufficientto achieve 100% conjugation efficiency using the SSNPP cross-linker(FIG. 7). A comparison of the time course of the reaction of DM1 withantibody that had been modified with SSNPP or SPP is shown, for example,in FIG. 8. In each case the modified antibody was treated with a1.1-fold molar excess of DM1 per mole of linker incorporated. Thereaction with the SSNPP-modified antibody is considerably faster thanwith the SPP-modified antibody (FIG. 8). Even, a molar excess of1.7-fold is not sufficient to achieve a similar efficiency using SPP.The ability to use 1) a lower molar excess of DM1 and 2) fewer linkersper antibody allows a reduction in the amount of drug needed to achievea target DM1 to antibody ratio by as much as 50% when using SSNPP as thecross-linker instead of SPP.

The increased efficiency of conjugation using the SSNPP linker isaccomplished without compromise in the monomeric character of theconjugate and in the amount of unconjugated (free) drug associated withthe antibody conjugate. SEC analysis is used to determine the amount ofmonomer, dimer, trimer, or higher molecular weight aggregates. Typicalresults of greater than 90% monomer were obtained with either linker asshown in Table 1. The level of unconjugated drug was measured by reversephase HPLC analysis of the conjugate sample. The percent free drug foreither reaction was less than 2%. In addition, shorter conjugationreaction times are possible with SSNPP compared with SPP (U.S. Pat. No.6,913,748), which may decrease loss of some antibodies that aresensitive to prolonged exposure to organic solvent required in theconjugation reaction. Shorter reaction times should also decrease drugloss due to DM1 dimerization, which is a competing side reaction duringconjugation. The resulting increases in yield and reduced side reactionsshould further contribute to reduced DM1 requirements.

The enhanced rate and efficiency of conjugation when using SSNPP wasalso observed when conjugating a different drug to the antibodydemonstrating the broad applicability of this new linker reagent. Acomparison of conjugation efficiencies using SSNPP and SPP whenconjugating the N901 antibody with the DNA-alkylating drug, DC4, aCC-1065 analogue, is shown, for example, in Table 3. By 2 hours thereaction using the SSNPP cross-linking reagent was complete whereas thereaction using the SPP reagent showed only 73% completeness by 2 hoursand significant incorporation of drug beyond 2 hours (91% after 18hours). Only much prolonged reaction times may lead to 100%completeness.

Example 3. In Vitro Cytotoxicity Evaluation of Maytansinoid Conjugatesof Antibodies with Thioether (Non-Cleavable) and Disulfide LinkersContaining Sulfonate Group

The cytotoxic effects of the antibody-maytansinoid conjugates withthioether and disulfide linkers containing a sulfonate group_weretypically evaluated using a WST-8 cell-viability assay after a 4-5 daycontinuous incubation of the cancer cells with the conjugates. Theantigen-expressing cancer cells (˜1000-5000 cells per well) wereincubated in 96-well plates in regular growth medium containing fetalbovine serum with various concentrations of the antibody-maytansinoidconjugates for about 5 days. The WST-8 reagent was then added and theplate absorbance was measured at 450 nm after ˜2-5 h. The survivalfraction was plotted versus conjugate concentration to determine theIC₅₀ value (50% cell killing concentration) of the conjugate.

FIGS. 60 and 61 show the enhancement in cytotoxicities of Anti-CanAg(huC242)—maytansinoid conjugates with the sulfonate-containingdisulfide-bonded linker (huC242-Sulfo-SPDB-DM4) bearing 6.0 to 7.6maytansinoid/Ab compared to the conjugate with 3.3 maytansinoid/Abtoward CanAg-positive COLO205 and COLO205-MDR cells. The potency of theconjugates with high maytansinoids loads indicate that the decoration ofthe antibody with up to 8 maytansinoid molecules did not affect theconjugate binding to the target COLO205 cells.

FIG. 64 shows the cytotoxic activities of anti-CanAg Ab-maytansinoidconjugates with similar maytansinoid load against CanAg antigen-positiveCOLO205-MDR cells. The presence of sulfonate group in disulfide linkersignificantly enhanced conjugate potency toward these multiple drugresistant cells. The enhanced potency of the sulfonate-linked conjugateis a novel finding and potentially very promising for therapeuticapplications.

FIG. 63 shows the cytotoxic activities of anti-EpCAM Ab-maytansinoidconjugates with similar maytansinoid load against EpCAM antigen-positiveCOLO205-MDR cells. The presence of a sulfonate group in disulfide linkersignificantly enhanced conjugate potency toward these multiple drugresistant cells. The enhanced potency of the sulfonate-linked conjugateis a novel finding and potentially very promising for therapeuticapplications.

FIG. 64 shows the cytotoxic activities of anti-EpCAM Ab-maytansinoidconjugates with similar maytansinoid load against EpCAM antigen-positiveHCT cells. The presence of a sulfonate group in the disulfide linkersignificantly enhanced conjugate potency toward these multiple drugresistant cells. The enhanced potency of the sulfonate-linked conjugateis a novel finding and potentially very promising for therapeuticapplications.

FIG. 65 shows the cytotoxic activities of anti-EpCAM Ab-maytansinoidconjugates with similar maytansinoid load against EpCAM antigen-positiveCOLO205-MDR cells. The presence of a sulfonate group in the thioetherlinker significantly enhanced conjugate potency toward these multipledrug resistant cells. The enhanced potency of the sulfonate-linkedconjugate is a novel finding and potentially very promising fortherapeutic applications.

Example 4. Comparison of In Vivo Anti-Tumor Activity of theAnti-EpCAM-Maytansinoid Conjugates, B38.1-SPDB-DM4 andB38.1-Sulfo-SPDB-DM4, on Colon Cancer, COLO205 and COLO205-MDR,Xenografts

The anti-tumor effect of B38.1-SPDB-DM4 and B38.1-sulfo-SPDB-DM4conjugates was evaluated in a xenograft model of human colon carcinoma,COLO205 and COLO205-MDR, which was engineered to overexpressP-glycoprotein. The cells were injected subcutaneously in the area underthe right shoulder of SCID mice. When the tumor's volume reachedapproximately 200 mm³ in size, the mice were randomized by tumor volumeand divided into three groups. Each group was treated with a single i.v.bolus of either B38.1-SPDB-DM4 (10 mg conjugate protein/kg),B38.1-sulfo-SPDB-DM4 (10 mg conjugate protein/kg) or phosphate-bufferedsaline (vehicle control). Tumor growth was monitored by measuring tumorsize twice per week. Tumor size was calculated with the formula:length×width×height×½.

The changes in volumes of individual COLO205-MDR tumors are shown inFIG. 66. Treatment with either conjugate resulted in significant tumorgrowth delay. B38.1-sulfo-SPDB-DM4 was more efficacious thanB38.1-sulfo-SPDB-DM4 in this human colon cancer xenograft model.

The changes in volumes of individual COLO205 tumors are shown in FIG.67. Treatment with either conjugated resulted in significant tumorgrowth delay. Two of six animals treated with B38.1-sulfo-SPDB-DM4 hadcomplete tumor regressions. Thus, B38.1-sulfo-SPDB-DM4 was significantlymore efficacious than B38.1-sulfo-SPDB-DM4 in this model.

Example 5. Synthesis of Procharged Linkers (CX1-1)

Z-Gly-Gly-Gly-β-Ala-OtBu

1.3 g (4.0 mmol) of Z-Gly-Gly-Gly-OH, 0.583 g (4.0 mmol) oftert-butyl-3-aminopropionate 0.651 g (4.25 mmol) of hydroxybenzotriazoleand 0.81 g (4.23 mmol) of N-(3-dimethylaminopropyl)-N′-ethylcarbodiimidehydrochloride were weighed into a 50 mL flask then dissolved in 20 mL ofdimethylformamide with magnetic stirring under a nitrogen atmosphere.After 3 hours the reaction mixture was purified in 5 mL portions byreverse phase HPLC using a 5.0 cm×25 cm C18 column. The column was runat 100 mL/min with deionized water containing 0.3% formic acid 5%acetonitrile for 10 min followed by a 15 min linear gradient from 5%acetonitrile to 90% acetonitrile. Product fractions (retention time of19 min) were combined and solvent was removed by rotary evaporationunder vacuum to give 1.35 g (75%) of the title compound. ¹H NMR(d₆-DMSO) 8.16 (t, J=5.2 Hz, 1H), 8.10 (t, J=5.2 Hz, 1H), 7.82 (t, J=5.2Hz, 1H), 7.25-7.4 (m, 5H), 5.04 (s, 2H), 3.74 (d, J=5.6 Hz, 2H), 3.67(t, J=6.4 Hz, 4H), 3.25 (q, J=6.1 Hz, 2H), 2.35 (t, J=6.8 Hz, 2H), 1.39(s, 9H). ¹³C NMR (d₆-DMSO) 170.45, 169.61, 169.00, 168.63, 156.49,136.94, 128.30, 127.76, 127.69, 79.89, 65.51, 43.56, 42.10, 41.90,34.89, 34.78, 27.70. HRMS (M+Na⁺) Calc. 473.2012 found 473.1995.

H-Gly-Gly-Gly-β-Ala-OtBu

1.3 g (2.89 mmol) of Z-Gly-Gly-Gly-β-Ala-OtBu was disolved in 80 mL of95:5 methanol:deionized water in a 250 mL parr shaker flask to which wasadded 0.12 g of 10% palladium on carbon. The flask was shaken under ahydrogen atmosphere (42 PSI) for 7 hours. The mixture was vacuumfiltered through celite filter aid and the filtrate was concentrated byrotary evaporation under vacuum to give 0.88 g (96%) of the titlecompound. ¹H NMR (d₆-DMSO) 8.12 (t, J=1.6 Hz 2H), 8.08 (t, J=1.6 Hz,1H), 3.75 (s, 2H), 3.64 (d, J=5.9 2H), 3.28 (bs, 2H), 3.24 (q, J=6.0 Hz,2H), 3.13 (s, 2H), 2.35 (t, J=6.8 Hz, 2H), 1.39 (s, 9H). ¹³C NMR(d₆-DMSO) 173.38, 170.46, 169.18, 168.70, 79.89, 44.65, 41.95, 34.88,34.78, 27.71. HRMS (M+H⁺) Calc. 317.1825, found 317.1801.

Mal-Gaba-Gly-Gly-Gly-β-Ala-OtBu

513 mg (2.8 mmol) of 4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)butanoicacid, 800 mg (0.2.8 mmol) tert-butyl3-(2-(2-(2-aminoacetamido)acetamido)acetamido)propanoate and 583 mg (3.0mmol)N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride weredisolved in 12 mL of dimethyl formamide and stirred for 3 hours. Thereaction mixture was purified in four equal portions by reverse phaseHPLC using a 5.0 cm×25 cm C18 column. The column was eluted at 100mL/min with deionized water containing 0.3% formic acid and 5%acetonitrile for 10 min followed by a 13 min linear gradient from 5%acetonitrile to 33% acetonitrile. Product fractions (retention time of21 min) were combined and solvent was removed by rotary evaporationunder vacuum to give 832 mg (62%) of the title compound. ¹H NMR(d₆-DMSO) 8.10-8.16 (m, 2H), 8.07 (t, J=4.8 Hz, 1H), 7.0-7.15 (m, 1H),3.747 (t, J=6.0 Hz, 3H), 3.64 (d, J=5.6 Hz, 2H), 3.41 (t, J=6.8, 2H),3.1-3.33 (m, 1H), 3.19-3.26 (m, 2H), 2.348 (t, J=6.8, 2H), 2.132 (t,J=7.2 Hz, 2H), 1.67-1.76 (m, 2H), 1.39 (s, 9H). ¹³C NMR (d₆-DMSO)171.80, 170.98, 170.39, 169.48, 168.96, 168.56, 134.37, 79.83, 42.05,41.83, 37.38, 34.82, 34.71, 32.26, 27.83, 23.95. HRMS (M+Na^(t)) Calc.504.2070 found 504.2046.

Mal-Gaba-Gly-Gly-Gly-β-Ala-OH

820 mg (1.7 mmol) of Mal-Gaba-Gly-Gly-Gly-β-Ala-OtBu was disolved in 9.0mL of 95:5 trifluoroacetic acid: deionized water and magneticallystirred for 3 hours. Solvent was removed by rotary evaporation undervacuum to give 730 mg (100%) of the title compound. ¹H NMR (d₆-DMSO)12.1 (bs, 1H), 8.05-8.20 (m, 3H), 7.82 (t, J=6.0 Hz, 1H), 7.00 (s, 2H),3.71 (t, J=6.0 Hz, 4H), 3.65 (d, J=6.0 Hz, 2H), 3.41 (t, J=7.2 Hz, 2H),3.26 (q, J=5.6 Hz, 2H), 2.38 (t, J=7.2 Hz, 2H,), 2.14 (q, J=8.0 Hz, 2H),1.67-1.77 (m, 2H). ¹³C NMR (d₆-DMSO) 172.70, 171.83, 171.01, 169.50,168.99, 168.51, 134.38, 42.07, 41.84, 36.75, 34.70, 33.69, 32.28, 23.97HRMS (M+Na^(t)) Calc. 448.1444 found 448.1465.

Mal-Gaba-Gly-Gly-Gly-β-Ala-ONHS (CX1-1)

76 mg (0.18 mmol) of Mal-Gaba-Gly-Gly-Gly-β-Ala-OH, 72 mg, (0.376 mmol)of N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride and 66mg (0.575 mmol) of N-hydroxysuccinimide were disolved in 1.0 mL ofdimethylformamide with magnetic stirring. After 2 hours the reactionmixture was purified in two equal portions by reverse phase HPLC using a1.9 cm×10 cm C8 column. The column was eluted at 18 mL/min withdeionized water containing 0.3% formic acid and 5% 1,4-dioxane for 3 minfollowed by a 15 min linear gradient from 5% 1,4-dioxane to 30%1,4-dioxane. Product fractions (retention time 6.5 min) were collectedin a flask and immediately frozen in a dry ice acetone bath. Solvent wasremoved by lyophilization at ambient temperature to give 40 mg (42%) ofthe title compound. ¹H NMR (d₆-DMSO) 8.08-8.11 (m, 3H), 7.99 (t, J=6.4Hz, 1H), 7.00 (s, 2H), 3.6-3.75 (m, 6H), 3.0-3.2 (m, 4H), 2.84 (s, 4H),2.13 (t, J=7.6 Hz), 1.83-1.93 (m, 2H), 1.69-1.72 (m, 2H).HRMS (M+Na⁺)calc. 545.1608 found 545.1638.

Z-Glu(OtBu)-Gly_Gly-NH₂

40 mL of Dimethyl formamide was added to 2.52 g (7.47 mmol) ofZ-Glu(OtBu)-OH, 1.3 g (8.49 mmol) of hydroxybenzotriazole, 1.3 g (7.76mmol) of H-Gly-GlyNH2, and 1.52 g (7.93 mmol) ofN-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride. 2.5 mL(14.3 mmol) of diisopropyl ethyl amine was added and the reaction wasstirred over night. The reaction mixture was purified in three equalportions by direct injection on a preparative 5 cm×25 cm C18 HPLCcolumn. The column was run at 100 mL/min with deionized water containing0.3% formic acid with 5% acetonitrile for 10 min followed by a 15 minlinear gradient from 5% acetonitrile to 90% acetonitrile. Productfractions (retention time 18-20 min) were combined and solvent wasremoved by rotary evaporation under vacuum to give 2.9 g (83%) of thetitle compound. ¹H NMR (400 MHz, CDCl₃) δ 7.79 7.68 (m, 1H), 7.64 (s,1H), 7.27 (q, J=4.9, 5H), 6.90 (s, 1H), 6.42 (s, 1H), 6.35 (d, J=6.8,1H), 5.08 (d, J=12.0, 1H), 4.98 (d, J=12.2, 1H), 4.20 (dd, J=12.9, 7.6,1H), 3.84-3.95 (m, 2H), 3.83 (d, J=5.0, 2H), 2.42-2.19 (m, 2H), 2.07 (d,J=6.9, 1H), 1.96-1.83 (m, 1H), 1.39 (s, 9H). ¹³C NMR (101 MHz, DMSO) δ171.79, 171.65, 170.82, 168.87, 163.04, 156.08, 136.86, 128.31, 127.74,79.64, 65.58, 53.96, 42.17, 41.81, 31.25, 27.73, 27.01.

H-Glu(OtBu)-Gly-Gly-NH₂

940 mg (2.09 mmol) of Z-Glu(OtBu)-Gly-GlyNH2 was dissolved in 40 mL of95:5 methanol:de-ionized water in a 250 mL glass PARR hydrogenationshaker flak. 222 mg of 10% palladium on carbon was added to the flaskand the contents were hydrogenated with shaking under hydrogen (40 PSI)for 4 hours. The mixture was vacuum filtered though celite filter aidand solvent was removed from the filtrate by rotary evaporation to give640 mg (94%) of the title compound. ¹H NMR (400 MHz, DMSO) δ 4.03 (s,1H), 3.75 (d, J=3.3, 2H), 3.63 (s, 2H), 3.30-3.22 (m, J=3.6, 1H),3.14-3.10 (m, 1H), 2.27 (t, J=7.9, 2H), 1.84 (td, J=13.6, 7.4, 1H), 1.63(td, J=15.0, 7.5, 1H), 1.39 (s, 9H). ¹³C NMR (101 MHz, MeOD) δ 176.53,174.24, 172.00, 170.32, 81.82, 55.21, 43.64, 43.16, 40.44, 32.31, 30.45,28.41. HRMS (M+H⁺) Calc. 317.1825 found 317.1800.

E001008-28 Mal-Gaba-Glu(OtBu)-Gly-Gly-NH₂

603 mg (1.9 mmol) of H-Glu(OtBu)-Gly-Gly-NH2, 372 mg (2.03 mmol) ofMal-Gaba-OH and 430 mg (2.24 mmol) ofN-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride weredissolved in 4.5 mL of dimethyl formamide and 800 μL of dichloromethane.The reaction was stirred for 3 hours at ambient temperature. Thereaction mixture was purified in two equal portions by direct injectionon a preparative 5 cm×25 cm C18 HPLC column. The column was run at 100mL/min with deionized water containing 0.3% formic acid 5% acetonitrilefor 10 min followed by a 15 min linear gradient from 5% acetonitrile to90% acetonitrile. Product fractions (retention time 17.4-19.2 min) werecombined and solvent was removed by rotary evaporation under vacuum togive 2.9 g (83%) of the title compound. ¹H NMR (400 MHz, CDCl₃) δ 8.16(t, J=5.7, 1H), 8.06 (d, J=7.4, 1H), 7.99 (t, J=5.8, 1H), 7.19 (s, 1H),7.06 (s, 2H), 4.18 (dd, J=13.4, 7.9, 1H), 3.70 (d, J=5.7, 2H), 3.62 (d,J=5.8, 2H), 3.42-3.37 (m, 2H), 2.23 (t, J=8.0, 2H), 2.12 (dd, J=8.1,6.4, 2H), 1.87 (dt, J=14.2, 7.9, 1H), 1.70 (dt, J=13.7, 6.8, 2H), 1.38(s, 9H). ¹³C NMR (101 MHz, DMSO) δ 173.12, 171.77, 171.65, 171.03,170.79, 168.89, 134.43, 79.62, 52.02, 42.14, 41.81, 36.80, 32.29, 31.22,27.73, 26.95, 24.02. HRMS (M+Na^(t)) Calc. 504.2070 found 504.2053.

Mal-Gaba-Glu(OH)-Gly-Gly-NH₂

105 mg (0.218 mmol) of Mal-Gaba-Glu(OtBu)-Gly-Gly-NH2 was dissolved in 5mL of 95:5 trifluoroacetic acid:de-ionized water and magneticallystirred for 2 hours. Solvent was removed by rotary evaporation andresidue was taken up in 6 mL acetonitrile+1.5 mL toluene to give asuspension. Solvent was evaporated from the suspension by rotaryevaporation under vacuum to give 92 mg (100%) of the title compound. ¹HNMR (400 MHz, DMSO) δ 6.99 (s, 2H), 4.18 (dd, J=8.2, 5.7, 1H), 3.70 (s,2H), 3.61 (s, 2H), 3.40 (t, J=6.8, 2H), 2.26 (t, J=7.8, 2H), 2.19-2.05(m, 2H), 1.90 (dt, J=13.7, 7.4, 1H), 1.73 (dt, J=14.2, 7.5, 3H). ¹³C NMR(101 MHz, DMSO) δ 173.76, 171.72, 170.99, 170.70, 168.81, 134.37, 52.00,41.97, 41.63, 36.75, 32.19, 29.95, 26.79, 23.93.

Mal-Gaba-Glu(ONHS)-Gly-Gly-NH₂

94 mg (0.22 mmol) of Mal-Gaba-Glu(OH)-Gly-Gly-NH₂, 75 mg (0.65mmol)N-hydroxysuccinimide and 110 mg (0.57 mmol) ofN-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride weremagnetically stirred in 1 mL of dimethyl formamide for 3 hours. Thecrude reaction mixture was purified in three equal portions by directinjection on a 1.9 cm×10 cm C8 column. The column was run at 18 mL/minwith deionized water containing 0.3% formic acid and 5% 1,4-dioxane for3 min followed by an 18 min linear gradient from 5% 1,4-dioxane to 30%1,4-dioxane. Product fractions (retention time 7.3 min) were collectedin a flask and immediately frozen in a dry ice/acetone bath. Thecombined frozen material was lyophilized to give 80 mg (70%) of thetitle compound. ¹H NMR (400 MHz, DMSO) δ 8.20 (t, J=5.4, 1H), 8.13 (d,J=7.3, 1H), 8.03 (t, J=5.6, 1H), 7.21 (s, 1H), 7.06 (s, 1H), 7.01 (s,2H), 4.29 (dd, J=13.7, 6.5, 1H), 3.84-3.69 (m, 2H), 3.63 (d, J=5.7, 2H),3.57 (s, 2H), 3.41 (t, J=6.8, 2H), 2.81 (s, 3H), 2.78-2.69 (m, 2H), 2.15(dd, J=9.1, 6.2, 1H), 2.10-1.95 (m, 1H), 1.88 (dt, J=17.0, 7.5, 1H),1.73 (dd, J=14.0, 6.9, 2H). HRMS (M+Na⁺) Calc. 545.1608 found 545.1627.

Example 6. Synthesis of Positively Charged Linker

3-(Dimethylamino)dihydrothiophen-2(3H)-one (217)

3-aminodihydrothiophen-2(3H)-one hydrochloride (213) (1.0 g, 6.51 mmol)and formaldehyde (3 ml, 40.3 mmol) in methanol was added sodiumcynoboronhydride (0.409 g, 6.51 mmol) in five portions in 1 h. Afterbeing stirred for 2 h, the mixture was evaporated, redissolved in EtAc,washed with 1 M NaH₂PO₄, dried over MgSO₄, filtered, concentrated andpurified by SiO₂ column eluted with MeOH/DCM (1:30) to afford 0.812 g(86%) of the title compound. 1H NMR (CDCl₃) 3.49 (dd, 1H, J=6.3, 12.1Hz), 3.24 (m, 2H), 2.42 (s, 6H), 2.38 (m, 1H), 2.21 (m, 1H); 13C NMR206.58, 73.24, 41.62, 27.47, 25.51; ESI MS m/z+146.0 (M+H), 168.0(M+Na).

2-(dimethylamino)-4-(pyridin-2-yldisulfanyl)butanoic Acid (218)

3-(dimethylamino)dihydrothiophen-2(3H)-one (217) (0.95 g, 6.54 mmol) wasstirred in 15 ml of 0.5 M NaOH and 10 ml of methanol solution for 30min, nutralized with H₃PO₄ to pH 7.2, and 1,2-di(pyridin-2-yl)disulfane(5.76 g, 26.2 mmol) in 50 ml of methanol was added. The mixture wasstirred overnight, concentrated, washed with EtAc and the aquouessolution was loaded on C-18 column, eluted from 5% methanol in 0.01%formic acid to 30% methanol in 0.01% formic acid to afford the titleproduct (368 mg, 20.65% yield). ¹H NMR (CD1₃OD) 8.31 (dd, 1H, J=0.7, 4.7Hz), 7.77 (m, 2H), 7.15 (dd, 1H, J=0.8, 5.8 Hz), 3.22 (m, 1H), 2.85 (m,2H), 2.51 (s, 6H), 2.05 (m, 2H); ¹³C NMR 175.00, 161.28, 150.46, 139.40,122.60, 121.49, 71.20, 42.46, 36.29, 29.88; ESI MS m/z+272.9 (M+H),295.0 (M+Na).

2,5-dioxopyrrolidin-1-yl2-(dimethylamino)-4-(pyridin-2-yldisulfanyl)butanoate (219)

2-(dimethylamino)-4-(pyridin-2-yldisulfanyl)butanoic acid (218) (92 mg,0.338 mmol), 1-hydroxypyrrolidine-2,5-dione (65 mg, 0.565 mmol) and EDC(185 mg, 0.965 mmol) was stirred in 3 ml of DMA at 50° C. overnight. Themixture was evaporated and purified on a SiO₂ column eluted withfrom1:10 to 1:4 of methanol/CH₂Cl₂ to afford 43 mg (35%) of the titleproduct. ¹H NMR (CD1₃OD) 8.40 (m, 1H), 7.83 (m, 2H), 7.22 (m, 1H), 3.34(m, 1H), 2.82 (m, 2H), 2.75 (s, 4H), 2.66 (s, 6H), 1.98 (m, 2H); ¹³C NMR177.21, 161.78, 161.12, 150.68, 139.37, 122.70, 121.66, 70.80, 44.16,43.15, 36.06, 27.38; ESI MS m/z+369.2 (M+H).

Example 7. Preparation of huMy9-6-CX1-1-DM1 Procharged Linker Conjugates

The following stock solutions were used: 39.6 mM DM1 in DMA; (2) 17.8 mMsolution of CX1-1 linker in DMA; (3) 200 mM succinate buffer pH 5.0 with2 mM EDTA. The reaction mixture containing between 8, 12 or 16equivalents of linker to antibody were added to a solution of theantibody at 4 mg/ml in 90% phosphate buffer pH 6.5)/10% DMA and allowedto react for 2 h at 25° C. pH 5.0, followed by reaction with DM1.

The Ab conjugate was separated from excess small molecule reactantsusing a G25 column equilibrated in PBS pH 7.4. The purified conjugatewas allowed to hold for 2 d at 25′C to allow any labile drug linkages tohydrolyze and then the conjugate was further purified from free drug bydialysis in PBS overnight, and then 10 mM histidine/130 mM glycinebuffer pH 5.5 (1× o/n). The dialyzed conjugate was filtered using a 0.2um filter and assayed by UV/Vis to calculate number of maytansinoids perAb using known extinction coefficients for maytansinoid and antibody at252 and 280 nm. The recovery was ˜70% and number ofmaytansinoids/antibody measured for each conjugate ranged from 3.7 to6.8 depending on the linker excess used.

Example 8. In Vivo Pharmacokinetics

The plasma pharmacokinetics of charged Sulfo-Mal linker conjugates of ahumanized antibody C242 with ³H-labeled-DM4 (3.5 and 6.4 DM4/Ab) in CD-1mice were analyzed by antibody ELISA and by ³H-counting (FIGS. 72A and72B). The Ab-Sulfo-Mal-[³H]-DM4 conjugates bearing 3.5 and 6.4 D/A weredosed i.v. at 12.9 and 7.9 mg/kg (antibody dose) respectively. Theantibody values of plasma samples were measured by ELISA (based oncapture using goat-anti-huIgG antibody and detection usingdonkey-anti-huIgG antibody-horseradish peroxidase conjugate) and by³H-counting (scintillation counting). FIG. 72 A shows that these twomeasurements of conjugate concentrations by ELISA and by ³H-countingshowed similar values for each conjugate. Both the 3.5 and 6.4 D/AAntibody-Sulfo-Mal-DM4 conjugates showed good plasma stability over 4weeks with half-life of approximately 14.9 days and 9.7 daysrespectively, which are similar to the half-life of approximately 11.8days for the unconjugated antibody. The DM4/Ab ratio of the twoAb-Sulfo-Mal-DM4 conjugates (initially 3.5 and 6.4 D/A) were also stableover 4 weeks in plasma circulation, importantly even at the relativelyhigh 6.4 D/A load (FIG. 72 B). The half life of Sulfo-Mal-linked huC242Ab-Sulfo-Mal-DM4 conjugate with 3.5 D/A load dosed at 12.9 mg/kg was14.9 days (AUC=38449 hr.μg/mL), compared to a half life of 12.6 days(AUC=25910 hr.μg/mL) for SMCC-linked huC242 Ab-SMCC-DM1 conjugate with asimilar 4.2 D/A load dosed at 12 mg/kg, and thus was much improved overthat of the SMCC conjugate (FIG. 72B).

TABLE 1 Comparison of SSNPP and SPP linker in the conjugation of N901antibody with DM1. Conjugation was conducted for 2 hours at theindicated pH using a 1.7-fold molar excess of DM1 per linker. % % SECAnalysis Linker/ DM1/ Effi- free Mon- Di- Tri- Linker pH Ab Ab ciencydrug omer mer mer HMW SSNPP 7.4 4.1 3.8 93 0.8 91.9 6.3 0.6 0.1 SPP 7.45.6 4.3 77 1.8 93.6 4.9 0.4 0.2 SSNPP 6.5 4.0 3.7 93 0.9 — — — — SPP 6.56.6 4.6 70 1.9 — — — —

TABLE 2 Reduced linker to antibody ratio required to reach target DM1 toantibody ratio with SSNPP as linker. Conjugation was conducted for 2hours at pH 7.4 using a 1.1-fold molar excess of DM1 per linker. LinkerLinker/Ab DM1/Ab SSNPP 4.2 4.3 SPP 5.6 4.3

TABLE 3 Comparison of SSNPP and SPP linker in the conjugation of N901antibody a with DC4. Conjugation was conducted for the indicated time atpH 7.4 using 1.4-fold molar excess of DC4 per linker. Linker Time, hLinker/Ab DC4/Ab % efficiency SSNPP  2 4.2 4.3 102 SSNPP 18 4.2 4.1  98SPP  2 5.6 4.1  73 SPP 18 5.6 5.1  91

The invention claimed is:
 1. A compound of formula (IV):

wherein: Y′ represents a functional group that enables reaction with acell-binding agent, wherein Y′ is N-hydroxysuccinimide ester; Drepresents a cytotoxic drug linked to the cell-binding agent by adisulfide, thioether, thioester, peptide, hydrazone, ester, ether,carbamate, or amide bond; one of R₁, R₂, R₃, R₄, R₉, and R₁₀ is acharged substituent selected from SO₃ ⁻or X-SO₃, and the rest are H; land m are each 0; n is 1; and Z is absent.
 2. The compound of claim 1,wherein the cytotoxic drug is a maytansinoid.
 3. The compound of claim2, wherein the cytotoxic drug is DM1 or DM4.
 4. The compound of claim 2,wherein the cytotoxic drug is DM4.
 5. The compound of claim 1, wherein Drepresents a maytansinoid drug linked to the cell-binding agent by adisulfide bond.
 6. The compound of claim 5, wherein the maytansinoiddrug is DM1 or DM4.
 7. The compound of claim 5, wherein the maytansinoiddrug is DM4.